rebuilding a rebuilt slant

If you want 10:1 CR, make sure you use new head bolts or head studs, then you'll need the dizzy to be regraphed, use a billet cam gear set, and around the 35-75 (3/4 Race as they were known in the day) mark for a cam with about 0.500" lift.....and balanced.
A 600 square bore, vac 2nd Holley will do the trick.
A good electronic ignition system too, MSD or IC&E....need a good strong spark to light the fire.