340 buildups

Thats an easy one.

340 with a good set of flat top pistons as close to zero deck as you can get them. If they are 68-71 replacement pistons you'll either need to shave them down about .020" or run a thick gasket to keep them from kissing the Magnum heads closed combustion chambers. You should end up with alittl eover 10:1 compression.

Leave the heads stock except for a good valve job and new valve springs.
For a cam Id look in to something like a Comp cams 270H or XE268

Edlebrock makes a air gap rpm intake for the mag heads or you can drill the heads to use a LA intake, Holley 750 double pumper will work good with the 4 speed but would work alittl ebetter with some 3.91s. You could use a 3310 750 Vac secondary if you dont want a mech secondary.

1-5/8" headers and a 2.5" exhaust.