I might have missed the "history" on this particular situation, but it kind of sounds like some maintenance and diagnostics could be in order.
Seems that all of the Chryslers we've had (with 383s and 400s) needed to have a valve job by about 85,000 miles. Usually #5 or #7 exhaust valve were having issues (i.e., "burnt"). That gradual loss of compression is not really noticed just driving around until it gets bad enough to make the idle rougher than it already might be. Then the loss of that one cylinder's power will cause lower vacuum as you will need to throttle deeper into it to get close to the prior power on hills, etc. Lower vacuum = poor fuel economy too.
A burnt/leaking valve can be detected with a vacuum gauge or holding a shop towel spread over the exhaust pipe exit. Instead of a steady and smooth gas flow, when the cylinder with the burnt valve fires, there will be an extra puff followed by an extra "inhale" function that will make the shop towel push out and pull in when that all happens. Of course, there's the "time honored" method of pulling the plug wire off while the engine's running, looking for weak cylinders. Just make sure you're insulated from the fender! Kind of a shadetree compression test.
I concur that 230 degrees in a pressurized cooling system is hotter than we'd like it to be, but not to the danger zone (by about another 35 degrees). Poor circulation, as mentioned, can result in that elevated operating temperature. Even in a decently maintained cooling system, we tend to gauge the cleanliness by what we see in the radiator tank, but what's in the engine block can be much different and restrict water flow with localized hot spots (which can also cause one cylinder to detonate slightly as other cylinders do not) that would not normally be there. Doing the "remove freeze plugs, flush block, clean up mess" routine I mentioned a while back is the best way to do it.
Remember, too, that using any commercial cooling system flush kits that use somewhat caustic chemicals to clean things out can also remove the scale and such from the radiator and heater core water passages, possibly taking off the protective coating of sorts (scaled buildup corrosion) that's been keeping them from leaking, not to mention core/freeze plugs too.
Retarded ignition timing can cause hotter running too. The degree can relate to how it all interfaces with other engine factors too.
I might be wrong, but if a carburetor's running so lean to cause problems with the valves and such, then the Chrysler Lean Burn system (which operated at about 18.0 to one instead of 14.8 to one (or richer) air/fuel ratio would have cooked all of the valves in the engine before they got out of the basic warranty back then. Similarly, if it's running that lean (and shouldn't be), there would be decreased power and possibly backfires under load, not to mention lean misfire and the smell of excessive hydrocarbon emissions out the tailpipe.
The steel valley pan intake gaskets which Chrysler used on the B/RB motors usually are pretty darn reliable. No real reason for them to deteriorate or rust as they don't carry any water anywhere. Humid or moist atmospheres maybe, but I haven't heard of any real problems in that area. Metal head gaskets can deteriorate with age if the cooling system might not have been maintained all of these years, but I don't recall any stock Chrysler V-8s having problems in that area either--unless there is some machining issue with the block or cylinder heads.
Compression test? As the old line Chrysler service mangager pointed out to me years ago, all the compression test will check is the top (compression) ring. It can still hold good compression and the oil rings can still have enough wear and age (including loss of tension) to not effectively scrape the oil from the cylinder wall. The other thing on a compression test is to use it as a point of reference, one cylinder to another cylinder, not looking for hard and fast numbers per se, but how they all relate to each other.
Valve jobs on "semi-worn" motors? No real problem, or at least not quite as much as many might perceive. In reality, all you do that will affect all of the cylinders on that bank is to replace the head gasket. The one cylinder that has the burnt valve will certainly have more compression than before, just as the other cylinders might as the machine shop might have checked them too and maybe hand lapped them in, but I did not or have not observed a fresh valve job to really change anything other than the engine will run smoother. No significant oil consumption changes either. Unless you specify it, many machine shops will not touch the other valve pairs (of the other cylinders) where there were no burnt valve issues or reasons to do work there.
In reality, if there are any engine wear issues, doing a full rebuild with a competent machine shop doing the work is the best way out. It's certainly more expensive, and can be moreso if you line hone, set the deck surface dimension, bore, finish power hone, and otherwise replace/recondition every other aspect of the engine in addition to the normal "rings/bearings" overhauls. Just depends on what you want to spend. In some cases, the least spent is the best way out, but in other cases it really takes more to make things right again.
Just some thoughts from my experiences and observations over the years. Your similar experiences might have been different, which I fully respect also.
In many cases, many performance problems are really pretty easy to fix, but it will take some time to trace them down in many cases. Using the proverbial "fine tooth comb" and leaving no leaf unturned. A sharp mechanic can usually know where to look, but some of the "younger" mechanics might take longer.
One of life's little joys is the way a fine running Chrysler V-8 runs and sounds, especially when the back half of the 4bbl carb is activated! Exercise due care and discretion, of course, in those potential situations.
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