Wow,
Good thinking Hardcore B,
I've been running a 304/640 ultradyne solid (fairly agressive) for 3 seasons, 385 passes with the same springs.
They are Crower #68346, installed height is 1.920 using the old MP "2 inch" Titanium retainers, yeilding 155 seat and 416 open. Rockers are 1.5 Ductile Iron Isky's...normal shift point is 6500, but it's seen 7550 on spray. I'll be replacing them soon, with another set of identical springs, they cost 145$ from my supplier, so they aren't cheap, but I'm happy with the results!!!

"Livin' in a powder keg and givin' off sparks" 4 Street cars, 5 Race engines