Dodge motorhome vin decoding?

I found a couple breakdowns of the truck chassis vins but why are there multiple options for engine displacement? The fifth digit has A=440-3 and D=440-1, what is the difference as I thought the dash number on the block was just designating a casting change?

http://www.dodgetalk.com/forums/archive/index.php/t-45054.html

The -3 engine is a premium engine. This number will not be the same as the casting revision number on the block.