at the top of this, are you saying that Hughes has the only retainers?
Currently the plan is to cut down the guides and use the Hughes retainers with stock rockers and I found trick flow springs rated/sized like the Hughes springs.
Thoughts?
hughes has a kit designed for just the thing you're trying to do here: hughes 1199 kit
it's good to .650 lift w/o coil bind, and the #'s will work up to .550 lift. so beyond cutting down your guide for clearance you should be good, without additional machine work needed to fit the springs.