if you have to use the 273 heads, then yes it would be good to bump the ex to a 1.60 valve and pocket port the bowl

I better head would be a closed chamber #302 318 head

cant hurt go with the 1.88 valve,but the shrouding is the hold up in flow..even with bore notches

I have just went 1.60 ex and hoged out the ex bowl/port on some back yard engines,that gave a good bit of pop to it for the effort

you gonna flow bench them?