I'm running some 906 heads that i had machined to fit viton seals, and had the original locating section cut so i could run dual valve springs. I don't have any locating cups on right now, and from the one spring distance i've measured (only need a .030 shim). It doesn't look like i'll have enough clearance to run a locating cup.
I got hardened shims (although i'm not sure every spring will need one)
Can i run without locating springs

Cam is Hyrdraulic flat tappet
Advertised Duration 268/276, Lift .494/.513