Thanks guys, seems it's pretty clear that 1.46" spring isn't enough, and the 1.55" works for multiple people and is in the ballpark. Sounds like the 10* retainers are preferred anyway. Jim- I assume all that would take is adding a 50 thou shim under the spring?

The 240 vs. 270 debate is something I hadn't really considered, my original thinking was I could reuse my shortblock, intake, rockers, cam and carb with the 240's, was trying to prevent further scope creep and wallet spending. 270's would add the intake expense, and at that point I think my 850 DP is too small, and I'm also worried that on a 446" the ports are too big for it to cruise cleanly at low speeds. It looks like they make more power everywhere above 4000 rpm though, and would be the clear choice for a 512.

I'll think on it further for sure.