350 small block

stock size valves
2.00 int an 1.55 ex
2.020 int and 1.55 or 1.6 ex

which would be best without loosing bottom end power will also be changing cam

I have run both 1.94/1.50 and 2.02/1.60 in 350s.
I would say it will depend how fast you want to spin it.
Stock size should be good to 5200rpm.