[ponyakr]

If you wanna keep the 350 shortblock in the car, then rebuild it, if it needs rebuilding.

If it does need rebuilding, but you don't wanna keep it. Find a 481988 block to build. You can go with a stock stroke 400, or one of several stroker assemblies.

Now that I think of it, you can also use the pre-'70 400 blocks, since the '74 X-body has the same front subframe, & uses the same motor mounts as 1st gen Birds.

Just don't get a "557" block.

The XX 481988 blocks are good, but I assume that most only have the holes drilled & tapped for the later model, 3-bolt mounts. A decent shop could drill & tap the holes, but that's just extra expense.

I suppose that what you choose to do will depend on what the 350 shortblock needs, and what kind of power you want for the type of driving you'll be doing.

Lots of options.