Advice Appreciated

Are you using the stock valve train, the mechanicals, or going with a hydraulic cam?

A 273 won't take much cam before it has a decent lope to it, and you probably don't want to lose too much cylinder pressure. A 340 Repro cam is likely the biggest you want to use, considering street use.

I'd also have a good chat with the machinist, and determine first if you are doing hydraulic or solid lifters, and then cam selection becomes far easier.