I used a 12V Makita to spin my oil pump, and it worked OK. I did use extra-thin oil (ATF, actually - I had several gallons given to me and I wanted to sort of flush out everything. Plus it's red and easy to see.) Also, I had (temporarily) plugged the bypass oil filter lines.
I do get oil flow to the rockers. It sounds to me like you have something plugged. Unhook the little tube from the block and see what's flowing....
Good luck!
George
