Engine mounts

I've done 2 A body SB to BB swaps. The cutting is easy. The amount you cut off is frightening. And when it's done the retaining ability is sketchy which is why they sell you a limiter strap.

Doing a K-member swap when the engine is out of the car is very easy. 4 bolts and the steering coupler.

What will also make this worthwhile for you is installing the engine and transmission and headers from underneath the car in one shot.