Need a plan - component selection for restoring 68 340 that runs on 91 oct

FWIW.. I have run higher CR's (SCR and DCR) with iron heads, but with quench, but still had to keep ignition timing under control, even with 93 octane. So this is all within normal bounds of tuning. Was not a drag racer.... it all worked happily for my uses: horsing around on the street, commuting, towing a light rally car, etc.