on a 1995 astro 4.3 only the end lifters will pump oil to rocker arm Why?

why would some 4.3 have positive stop rockers and others adjustable i tried loosen the rocker and oil did pump up and the engine ran better and then torque back to 20 ft. lbs. and the engine ran worst

For the same reason some astros came with steel wheels and others aluminum........Did you get a receipt for the heads? Return them for the correct ones.Good luck.

please explain the the mechanics when both designs will work on the same short block or do they make different short blocks for the two different designs.

Good luck..............