[Jac Mac]

Have you allowed for the preload in the lifter and head gasket thickness, plus have you put some engineers dye on the valve tip & cycled the crank/cam/valvetrain thru a couple of revolutions to check for a central wear pattern with this 8.8" pushrod installed[ Yes, a little tricky to do with a new hyd roller lifter-you will need some very light check springs on the valves and have to watch for lifter compression closely to enable this check]
Many hyd roller lifters are taller than the flat tappet version which could explain the pushrod length difference.