the ones ou812 has...has a longer skirt to fix the oiling problem of the lifter uncovering the oil gally and loosing pressure with high lift cams IIRC
they have pressure oiling to the roller needle bearings also IIRC
and the link bar is to the cam side and not to the block side IIRC
maybe he will chime in and give a skoolin on them
on a non roller block...IIRC
the block will have to be clearaced in line with the lifter for the link bars to clear the block on other roller type lifters and should be bushed with high lifts so the oil passage is not uncoved
IIRC
lot easier and cheapr to start with a roller block IMO
unless ya just gotta keep that engine block for some reason