I've used them on my last 2 big block stroker builds. But if you have an aftermarket block MP/World, check to see that it does not interfere with #5 maincap. The 512 I have now needed clearancing on the retainer; so I used the retainer that came with the block. I have never had a leak using them on the 470 and 528 hemi that I built a few years back. Plus you can buy replacement square O ring side seals seperate from Mancini.