LA 318 to Magnum 360 swap

I did a similar build (stock bottom end magnum) you should check clearances on rod and main bearings before dropping in. My motor looked beautiful and the cylinders still had cross hatching but I still had to do Rod and Main bearings before dropping in.

Go back to the junk yard and find a pre 1996 magnum 360 balancer, they had the six bolts holding the serpentine pulley on. That's what I did. Works great with no vibrations.