I run an IMCA Hobbystock. You can see it at
www.Galynx.com/Harvey
You aren't suppose to change the wheelbase length. IMCA has a wheelbase rule... Unibodies = 109" minimum
Full Frames = 107.5" minimum
( Makes no sense to me, ask IMCA why. )
But I have a couple of friends that have been talking to IMCA tech about the 2 DUSTERS that they are building right now. Sounds like we are going to get to move the wheelbase back 1" on IMCA Hobbystock dusters, ect by changing the leafspring mounts. This will effectively move the back tires back 1". I don't know for sure on any rule with the IMCA. Last year we could run the stock Holley off a 360/400 mopar. This year they outlawed them. This year... no rivits allowed in doors or front fenders. They change the rules often.
I personally run a dodge dart. I tell IMCA that it is a 1977 Dart. (VERY rare, Indead)
IMCA hasn't caught on to that one yet, or the DODGE stickers on MY duster. <grin>
P.S.-What is the wheelbase on a '77 dart?