Upgrade the heads to a set of 58CC combustion chamber heads from a late-1980's 305 4 barrel engine. They have the same combustion chamber volume as the 283 "Power Pack" heads used in the late 1950's and early 60's, and they're a lot easier to find in serviceable or easily-rebuildable condition than a set of 50-something year old heads. They also have the bolt holes on the ends of the heads for mounting accessories like an alternator or a power steering pump, etc.

If you choose to modify those heads, they can be fitted with 1.94" intake valves and 1.6" exhausts with a little tinkering. While you're at it, find a HEI distributor, an aluminum intake manifold and a Quadrajet carburetor for the same 305 engine. Do Not- - - -get tempted to go with an aftermarket manifold and carb! Find a set of ram's horn exhaust manifolds (definitely not headers!) with 2" exhaust pipe diameter and fit a set of free-flowing quiet mufflers. The 283 will manage 7,000+ RPM with a Comp Cams 268H hydraulic cam and a set of anti-pump-up lifters. Once you make 3 or 4 more posts you'll be able to send me a PM message and I'll share a trick that will make the stock HEI distributor work well up to 8K RPM or so. Without the mod it will spark-scatter above 5500 RPM and limit the top end that the 283 is capable of running.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!