Although I like a well spaced set of rockers, the issue you mentioned with the holddown bolt holes makes keeping the clearance during assemble tight, difficult. IMO, 0.015-0.030" tolerance should not be a big deal, but does take care installing. You can change your specs to 0.025-0.040" and that tends to be easier, but allows more movement.

Depending on application, the springs with hardened steel shims (0.015" or more) on each side of the spring, and between each rocker and holddown will work very well. For a low 6000 rpm engine, I think that will be fine. Over 7000 I would suggest going to the trouble, as well as all the rest for a motor spinning the valve train higher.