8.75 axle prep help

Ideally you would do this by mocking the parts up on the car with it sitting on a flat, level surface (suspension loaded) so that you can set the pinion angle relative to the transmission. Otherwise:

Temporarily install the chunk in the housing.

Set the housing on jack stands on a flat, level surface.

Put an angle finder on the flat edge of the pinion yoke and rotate the axle up or down till you have the desired pinion angle.

Locate the perches and make sure they are level relative to the floor, then clamp in place.

Double and triple check everything to make sure it hasn't moved. Weld the perches in place. If you don't have a good hot welder or welding experience then tack weld the perches in place and take it to someone who can finish the welds.

Doing all this out of the car may require you to use pinion wedges (shims) between the perches and springs after it's installed in the car to fine tune the pinion angle.

If the old perches were still on the axle you could use those for reference angles for welding on the new ones.

Also, be sure you check the spring locating hole in the new perches. Some are too big for the locating pin on the springs. If so, you'll need to weld a "bushing" in the hole. If I recall, one trick is to weld a 3/8" pipe nipple in the hole and grind flush. Then drill out the hole to the correct diameter. That's what I had to do.

Do an internet search for setting pinion angles.