I installed a pontiac seven blade clutch fan I bought off of ebay on my '67 w/ a 400. I don't think I used a spacer but the fit is perfect, and I used bolts on mine. I would have prefered to use studs, but I couldn't find any that were the right length. Even the ones I ordered from Ames weren't the right length. And when I talked to their tech guy he didn't have any answers for me either. I used bolts w/ loctite and no lock washers. I think the bolts had to be about 1.25" long or so(I can't remember for sure). So far so good--it hasn't gone through the radiator yet, and the bolts haven't moved either. Studs would be SO much easier. Getting everything lined up and putting the first bolts through the holes and started in the threaded pump flange is a major PITA--seriously it really sucks. Also with bolts they can't protrude through the back side of the water pump flange too far or you'll have clearance issues. Good Luck
