John F is right, now that they are available, buy them from J Mummert. However some scrub valves are adaptable to Y blocks. In the late 90's I did use Flaming River Scrub SS exhaust valves that were .200" longer than Scrub stock. It is also true that retainer groove is a little lower than stock Y block. I got around this by using Deep Isky retainers that allowed for the corrrect spring length. Avoid all this monkey motion by getting them from Mummert. At the time I inquired from Flaming River how to get custom made valves and the minimum order was something like 50 or so. John must have a deal like this with some manufacturer and buying them from him gives us all the benefit of haveing these kinds of parts available.