Cast iron, dual point, ball bearing vacuum advance Prestolite distributors only came on Commando / Charger 4 barrel 273's. The "Correct" 68 273 would have open chambered heads like the 318, slightly taller flat top pistons with 4 valve notches, a standard Chrysler distributor, and hydraulic lifter cam setup. What you have, may or may not be, a stock 273 2 barrel from a 1968 Belvedere. Closed chambered heads are typically less prone to detonation, but in a 273 closed chambers will give more compression. Which is going in the wrong direction for you.