The heads are "power pack" high compression items used on 265 and 283 engines- - - -with 58 CC combustion chamber volume and relatively small intake and exhaust valves. They provide plenty of compression pressure, but the gas flow is somewhat restricted due to the small valves. The intake will be from a mid to late 1960's 327, or more likely a 350 with an early version of the Quadrajet carbutretor. Later models did not have the slot for exhaust gas from the heat riser, or the oil filler tube at the front near the thermostat housing. If you wanted to upgrade the heads and intake to later production items, there are 58CC heads with bigger valves from a late 1970's or early 80's 305, and an aluminim Q Jet manifold that would be a bolt-on swap to the ones currently on the engine. 283's use a "small rod journal" crankshaft with a 2.00 inch diameter rod bearing and smaller diameter main bearings than later model 327 and 350 engines. The small bearings and slower slip speed between the crankshaft and the bearings make them capable of pretty reliable operation up to around 8K RPM with the right bearings, lightweignt valves, and strong valve springs. A well tuned 283 at high speed sounds like a bunblebee on steroids!
Jerry
