I know you are using a Norton tank and I am familiar with them having had an atlas for the last 36 years, I was just pointing out on my Norvin I didn't bother with any sort of restriction in the tank.
I don't know the size of the hole in the Norton return pipe inside the tank off hand and I don't use mine anyway, I have a cartridge filter in the tool box and the return from that goes straight across into the oil tank, the original return pipe is blanked off.
Would all Nortons have a restriction in the return pipe, surely the ones with the pressure fed rocker set up wouldn't need one ??