What motor to go with?

I'd find ones that have the hardened seats. Like 1973 and later castings.

587 I think are like that.

Keep in mind that some of the dyno engines in those magazines were tested on the notoriously happy westech dyno. If you think for a minute that a XE268H cammed, stock 2.02 headed compression 340 with an RPM intake will make 390+ hp, I got a bridge to sell you in Brooklyn. That set up is good for about 1hp/cu. Seen more than one built the same bust out 330-345hp in the 5600 RPM range with a 750DP on it. They backed up those numbers with 1/4 trap speed consistent with those 330-345 results. The articles are good for getting ideas of what might work well together, however, take the dyno number with a grain of salt.