Hi ,
I have both A 81pe175,x( last twin shock) and an 80 Rm125T(also last twin shock,)
some parts interchangeable, seat base is same part No. but different mounts and foam, but will bolt straight on,
tanks should also bolt up with the right mount plates
engines will bolt in either frame but not all parts are interchangeable athought some internal parts cane be used
ie clutch plates are the same but PE has more plates than RM therefore clutch baskets are not the same, etc
my RM has remote canister shocks PE standard
Rear wheel /brake setup Pe has brakes and sprocket together on same side for quicker removal,
If you need any specific info I can go and have a look if that helps.
cheers
Noel