273 4bbl, carb replacement?

I would before spending a dime play with the timing (advance it) until it pings
slightly under hard acceleration. Once you find this spot then retard it slightly and test it again for no ping. Then get a timing light check where the timing is for mechanical and vacuum limits. Is your 273 an original 2 barrel or 4? This will determine the
compression and what octane gas it will need. Retarded timing causes symptoms you
discribe.