When Walt installed the new small block in his 1967 Chevy K10 pickup, the new aluminum valve covers were a bit taller than the stock covers, and they were right against the firewall. Any little movement in the engine would cause these to rub. After much deliberation, he decided to install the stock valve covers. The only problem with the stock valve covers, though, is that they did not originally have any cutouts for breathers. So, after a little bit of drilling and welding, he modified the stock covers to accept breathers.