Rallycross

Hello, everybody.
....I have an unusual concern here and hope that the users here might be able to help me...
My son drives Rallycross, with an Audi Coupe type 89... built-in is an AAH engine with Quattro transmission....has built up the thing Rally-suitable for him....
...he has already been quite successful in the first season....naya, in the beginner class....but he has always been first....
...now we want to change the machine to "real" classes.....we have the possibility of an ABH motor complete with cable harness and control unit (but unfortunately with automatic transmission and thus no transmission for rally operation) etc. to acquire....
My question is, does the Type 89 Quattro gear fit mechanically to the ABH????...probably by necessary changing the flywheel etc???
...the motor mounts are secondary...we weld them ourselves...
...we also have an AQF engine that we could get...but I think this is going to be much more difficult...or???
I am grateful for every helpful answer.....
Thorsten