273 Commando with roller camshaft

"Ideally l’d like to build a mild 300 hp 273 that’s run nice on the street with a 4-speed and 3.23 gears."

That's do-able, but you'd be better off to use 915 J heads with 1.88 valves and port work, a solid roller bigger than the specs I posted for mine and a good dual plane intake, like an LD340 or an RPM Air Gap. Maybe consider custom flat top pistons that will get you to 10 or 10.5-1 compression with whatever CC's and gasket thickness you have if you use J heads. The 1.88 valves are all that will fit without notching the cylinder bores....and they barely fit. I had 1.88 intake valves put in my 302 heads, but if I had it to do over again I'd dig a pair of J heads out of my stash and work them....then build under them.

:thumbsup: