I'm kind of with you Leon - I was thinking .050-.060.
I didn't specifically measure the retainer to guide, but there's quite a bit there. Looked at it when I had the checker springs on it checking v/p. Good question tho.
Vic - these heads are a real headache when it comes to springs. The valves aren't very long to get the right geometry, and the spring pockets aren't very deep because they're right over the intake ports and there's no material there. I end up with only a 1.700 installed height. Finding a spring that will give me 300lbs of seat pressure that won't coil bind on me is a pain. The springs I've got coil bind at 1.035.
The cam I was running had like a 550 lift. (I think if they made and RV cam for a 392 hemi, this may be it
The cam I was looking at running has a 660 lift. I measured the actual valve travel at the keeper with correct lash and it came out to 623. That gives me an open spring height of 1.077 - only .042 away from coil bind.
Guess I'll order me another RV cam - it worked before - it'll work again...