What block are you using? If it is a stock unbushed block I wouldn't recommend them due to oil control. One problem I did have with them in a stock 400 block was the #2 and #4 cylinders on my engine poured oil out at max lift. Couple that with the fact that you are pressure feeding the rollers and IMO you need to have a bushed block to limit oil loss at the lifters. I got by with it last year but am having the block bushed right now.