We've got a 1960/235 with hyd. lifters that I had trouble with. I agree about checking the adjustment-might want to make sure the adjuster screws are not worn to a point. But since you said it had been rebiult I would think they're OK. Anyway-On ours I found that alot of the noise was from the rocker arn assembly when it was cold. Once it warmed up things got better. We ran an additional oil supply line from the by-pass filter housing around the engine to the side of the head. There's a 1/8 plug directly above the distributor and just below the valve cover that feeds into the oil gallary to the rockers. Made a lot of difference for us. Just make sure you use GOOD material to make this line with. If it breaks your oil is going to be pumped out of the engine.

Ryan