89 Ram underhood AC components on my 74 Duster.

I am not sure but you may have problems with the power steering pump and brackets. I tried to use the pump off a 87 Dodge truck on my 70 Duster 340 and I know it did not fit right, I ended up getting a rebuilt pump. The intake manifold is also different in the location of the thermostat housing and the compressor will not fit on old stile intake.
I ended up using a Classic Auto Air system and it fit much better till I put a air gap intake on it, I had to make 1 simple new bracket for it.
Hope this helps. Good luck.
Mike