Best bet is to fabricate your own motor mounts and trans mounts. id personally switch to a th350 to simplify the swap. You are probably going to have a difficult time finiding an adapter kit to mate an r154 to a 350 engine.
you could probably somehow use an ati adapter plate that you normally would use to adapt a 7m to a th350 and do it in reverse, but i am not sure if that would work 100% or not, and then you would have to play around with trying to get a clutch to work in there and flywheel, etc, im not sure it would work easily and with little money.