With all due respect, I believe that if you check the vehicle architecture between a Chrysler and Imperial in the '67-'73 time frame, you'll discover that the added wheelbase results in added rear seat leg room, meaning the floorpan stampings behind the front seat is where the wheelbase is compensated for, not in the front subframe/body area as mentioned. When looking at exhaust items for C-body Chryslers, that's when I determined this was what was going on as the front exhaust manifold lead pipes were all the same between Plymouth Fury, Dodge Polara, Chrysler Newport/300/New Yorker yet the pipes between the ball joint connection and the muffler were all different. Only reason for them to be different is the wheelbase difference between those cars (119", 122", 124").
Imperial bodies were longer in front of the front wheels and aft of the rear wheels, but that's just sheet metal hanging on the basic structure. One area that might affect the Imperials of the '67 era would be the isolated engine mounting structure that was unique to Imperials only that might affect some of the routing of the trans cooler lines. Where the engine and trans are would be the same regardless of the wheelbase and should have the same relationship to the cowl/firewall. If, as I mentioned, the fan shroud on the Imperial is longer than on the regular Chrysler C-body cars, that would mean the core support is farther forward on the Imperials, which has no relationship to the wheelbase specification.
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