This is exactly the problem I was having a while back that caused a series of posts about 235 differences. My motor is a '60 and it had an outside oil line running around the back of the motor when I bought it. No oil filter and we couldn't figure out why. When all was said and done, I found I was getting no oil to the rockers after putting it all back together and priming the oil pump. I ended up tearing it all the way down, including removing the cam and crank shafts. I found that the 2 intermediate cam bearings were burned from not getting oil. The rear oil gallery was blocked and not getting oil to the cam and, therefore, not to the rockers. I had removed the lifters before and put compressed air from the rocker feedpipe hole down through the center gallery that Chip mentioned. I had good air coming out to the lifters that way. That's not where the blockage was. I know this is getting long, but I'd bet this is the problem you're having. I tore the engine all the way down to a bare block and then tried compressed air through the oil pump outlet to the main oil gallery. Guess what? I had blockage at the rear main and oil couldn't go beyond that point to the crank or to the cam shaft and beyond. I then had a machine shop boil the block and we cleaned out the oil galleries. Put it all back together with a new cam since oil starvation had ruined the old one. Earlier this week, I primed the oil pump and am getting good oil to the rockers. You could try blowing air down to the lifter gallery, but I'd bet you have blockage down below and if you don't get it cleared, you will damage the cam shaft and probably more. Also, I was told that cam bearings have been known to turn to where the hole that allows oil through doesn't line up with the gallery (galley?). Mine wasn't turned, but that could also be the problem. Either way, you won't know until you get it torn down. I am very glad I went to the trouble and it was very satisfying doing the work myself. Pretty easy following the shop manual. Also, I found alot of sludge and rust dust in my water passages, so boiling helped that alot too. GOOD LUCK!
