974 heads... flow numbers

There are a couple issues with building a 273 - piston choice and head gasket choice. Both are critical because it's a small, short stroke engine and needs all the compression it can get. If it were me I wouldn;t sweat the .060 over. You could have it sonic tested to be sure for a lot less than sleeving all 8 but IMO it's probably fine. they were cast back when making them way thick wasn't a budget issue. I'd get a set of custom pistons with a flat top and good valve reliefs and plan to runa set of Cometic custom head gakets. Then you can design a tight small chambered engine that will make some decent power on pump gas. Otherwise you're spending more to cobble something together with what I'd call old and sub-standard parts. Use the 302 heads - upgrade the valves to 1.88/160, do a little basic clean up, and reduce the chamber to give you a true 10:1 with a tight (.030) quench distance. he .528 is a decent cam but much better can be had. I'd look for a modern solid profile with 225° or so @ .050" and lift around .500. Run a 318/360 Performer (easy to get at swaps - nobody likes them on 340/360s) and port match that to the heads. That Torker's not worth any time on this combo. I'd also recommend a new Thunder AVS 650 or Holley 570 Avenger. That would be my starting point. Even witht he gearing the trick is torque for a 273. It will rev just fine - but you need it to get the car moving and accelerate it. Not just make high rpm horsepower.