Crane Rocker arm clearance on Iron heads issue

I think you're headed in the right direction for sure. Hughes Engines sells a pile of rocker shims, so you should be able to get an assortment. I would run thin ones between the rocker hold downs and rockers, so be prepared to maybe even get different thicknesses of the thick spacers, too. Once you get "all that" done, then you should contact Mike at @B3RE (B3 Racing Engines) and he'll show you how to tell if your actual rocker geometry needs correcting and help you get it done. No sense in doing half of it and leaving the other half undone.