273 power? HOW?

The heads have smaller attaching bolts @ 5-16th. This makes a machining of the block to open the holes up for other heads a mandorty thing to do. HOWEVER;

You'll just need to pocket port the heads and backcutting the valves would be a good addition to low end flow. A light milling only to true yp the surface IF and only IF it needs it. The above idea of not to much compresion is very dead on and true. No sense looking for trouble.

Easy on the cam, a mild one will do wonders in the lil'engine that can.

The hardest part here is finding a intake to fit the heads. Look for old Edelbrock intake manifolds or go to offenhauser to get one.

Standard headers will fit and work well.

TWX, will that fit the earlier LA engines?