cnc-dude, those vw lifters can be had for $29.95 for a set of 8, so 2 sets would be required. that's still only $60.00; and i CAN have my existing n.o.s. iron cam ground with the vw profile for well under $100.00. that's bang for the buck that the rollers just can't hold a candle to. i have access to a CMM and we can plot the locations of the existing lifter bores and write a cnc program to bore them accurately once the block is bushed; that can't be any less accurate than the standards that GMC actually machined them to originally. i have actually seen the lifter bore bushing mod done to a vw waterboxer engine fitted with type 1 tappets, so it's not completely out of the question.
the block may or may not need spotfacing with my reduced base-circle cam. tooling would not be a real issue as i can make or modify most anything at school.
i'm also after valvetrain mass-reduction, and these fit the bill nicely.
