One thing to remember about the M-50 motored 325 is that the intake manifold is the envy of all the later M/S-52 motors. In the case of the S-52, a M-50 manifold swap will gain ~15-20hp alone. The later manifolds have narrower runners, and because they're ABS plastic can't be port matched, so they definetly don't have the gains that the M-50's see. So, if you found a good doner go for it.