Since I don't want my stock valve springs to float at around 4,000-4,500rpm's, I have heard that stock Lincoln/Zephyr springs are good for 6,000rpm's or better. If so I can get a set and wanted to know if this is correct. I plan to run my flattie at rpm's of no higher than 6,000. Also does anyone know if ford or mercury used adjustable tappets?