I have run roller rockers with needles (PRW) and with straight bushings (Hughes) on the same engine and had the same identical oil pressures.... 20psi hot idle and 72 psi hot running pressure. And the needle bearing rockers had an extra oil hole. To see what will happen, you need to examine the whole rocker oiling system with the restrictions that are there already, and also look at how tightly the needle cages are to the shafts and how that limits leakage out of the needle bearings.