Thanks, gentlemen...
Now we can get somewhere.
I had the problem that I couldn't take them off to compare because the van has to be on the road while I get the belts. And, unlike simpler older vehicles, it's very hard to get them on and off.
There is some coding in the numbers, it seems, the '605' and '444' part of the numbering appears to be the length of the belt to the first decimal place (ie. 605 is 60.5 inches) but it's possibly measuring the inside circumference as one listing gives the 605 belt length as 61.7" OC and the other the 444 is 45.07" OC.
I will report back when I have success.