I havnt been envolved in Off Road racing for a couple of years but if you want to enter class 5 in a full body car and you are changing the engine, use a lexus 4ltr v8
Reliability of these engines regardles of abuse is amazing.
As far as im aware the origional body shape must remain but everything else as long as they remain rwd can be changed.
I used to follow this car around being attatched somewhat to the family.
Class 1 with a Stock Toyota 3SGTE
Its awesome fun
What car do you plan on using?