When I build a board with inserts, I space the inserts so that either 6 or 6.5 inch spaced pads will mount. If 6.5, just skip an insert, the next one lines up pretty well.
Not sure if the spacing works out to exactly 6.5, maybe it's off by a hair, the pads still fit.
Also favor pads with slots instead of holes, ends worry about both pad fitting and stance angle. Even lets you use the next hole over if you blow out an insert, break a screw etc., with minimal stance change.