Call Hughes engine, IIRC they have retainers for magnum springs that allow more valve guide to retainer clearance. Their original retainers, which I have, only allows for about 20 thousandths clearance with a 512 lift cam.
Right, but these are aftermarket MP springs and won't work with the original Magnum retainers. These are a square spring while the OEM Magnum spring is a slight beehive and taper at the top. So the original retainers are too small to be used on these springs and anything that Hughes sells to work with the original springs won't work with them either.