.473 lift valve guide trim?

Also, if you do have an issue just because of the retainers and locks to guide clearance, you could use the Hughes set that they use for the magnum heads that give more clearance.
I can't imagine 318 spring retainers and locks causing a clearance problem, but spring bind might.
(I see that mentioned up there)

Just mock it up like rustycowl69 said and you'll know for sure.