Hi volume oil pump vs standard volume pump

Lifter bore diameter, at least in my '65 book, is .9050-.9058". (Small block and big block). There is just this spec.. not a separate service spec, at least that I can find. Lifter to bore clearance is listed at .0005-.0015"

Interestingly, this vintage of FSM lists oversize lifters being available, in .001", .008", and .030" oversizes. The FSM refers to reaming the bore out and using an oversize lifter if the lifter bore is worn or scored, so this wear matter was set up to be serviced.

Lifters sizes do vary within a range, so you might be able to ask a mfr to sort out a set of lifters sized at the large end of tolerance for you if the bores are just bit oversize. (We did this with a new Crane cam with the opposite problem of some of the larger production lifters not fitting in tight bores; Crane was quite obliging.)