I use a screw-in stud with a 3/4" long bottom as a quick gauge to be sure Im not getting carried away on the gasket match for intake ports.
At the very least get the valves backcut, I like 25 intake and 30 exhaust but everybody has their own theory on what angle to use. Good low buck mod that will pick up a few cfm.
Staying with the smaller valves will cause less problems with cutting through induction hardening on exhaust valve seats for sure. Larger valves will flow more and with same size port volume will increase port velocity not reduce it.
Theres better stock heads that will flow more but this is what youre working with. I think it boils down to how much do you spend before you could buy better different heads.
I would get one to practice on theres no shortage of junk 350 heads.