I have to check to make sure the rear axle is centered in the car. The springs are moved in and I need to weld the perches on. I am second guessing myself on this how does everyone recommend this be done. I have used a plumb bob on each frame rail and measured over to the flange to get an equal number on each side. It is a dana that Moser cut down so I know the offset is correct. I want to get this set and get the pinion angle set but before I move forward I wanted to bounce this off the Moparts crowd.

First find out what the axle is.. offset at the pinion then make sure the car is level then start checking with
the plumb bobs.. has the car EVER been in any crash

Mopar offset the engine, tranny and driveshaft to the passenger side to give the driver more room, if this is a stock floor type car I wouldn't center the rear end
If your trying to center the wheels in the wheel wells then use your measuring devices to get it where you like it on both sides before tacking the perches in place

It just depends what you are trying to center. Do you want the tires to have equal clearance on each side? If so, measure that. The fenders and the frame rails may not be in the same place on both sides of the car so you have to measure it and figure it out.

The pinion offset is correct I have measured that. Just trying to get the pinion in the correct spot and figured if I got the axle flanges equal distance from the frame rails it should put the pnion in the correct location right? It doesn’t look like the car was ever wrecked and I figured the frame was the best place to measure from..

You need to find the true centerline of the car then base it off that
EDIT
Also to think you have to have the pinion in the RIGHT place.. that can move to get the tires
under the car

Most body's are not on the true centerline. My way has been to center to outsides of the tires in the 1/4 panels. Dont be surprised if the axle measures off to one side more than the other. Centering it dead on may look like crap. As long as the axle is square to the centerline it bothers nothing.
Doug

the quality control of these cars when new was atrocious at best. it was not uncommon to find the rear 3/8-1/2" or more off center compared to each quarter panel opening.
as has already been said, square the axle to the centerline of the car, then move the rear side to side until it is equal to the frame rails.
this will maximize the available tire/wheel combo space.

I'll second the QC issues. In December of 1973, I ordered a 74 Challenger. It was delivered in February 74.

A good friend of mine ran an alignment shop. I transferred the Crager SS wheels with G60-14's I had on my old car an took it to him for an alignment. He found the car had 1/4" longer wheel base on one side.

I took the car back to the dealer and complained. They called the zone manager to see what could be done. He approved the repair.

The car also had terrible finish on the rear roof seams. It was ordered without a vinyl top and the rear roof seams were plainly visible. They offered to install vinyl. I told them, if I wanted vinyl, I would have ordered it that way. Again, the zone manager approved a rework of the rear roof pillars. Even after the rework, it was still visible, just not as apparent. I restored the car a couple of years ago and the body man I used fixed the seams and now it looks good.

Get the tires & wheels on the rear and center the tires in the wheelwell. Where the pinion ends up, it is what it is.
If the pinion isn't centered, no one will see it and it won't matter anyway. If the wheels aren't centered, it'll look like crap and everyone will see it.

But it doesn't look "original" !!! I have never seen an e-body car with well-finished roof seems - and I was around when they were new!! The quality absolutely sucked !

It seems there were many fitment issues - as evidenced by the gobs of seam sealer. On my 69 RR one of the rear spring hanger attachment brackets was put in crooked - something next to impossible to fix without major time and effort. If I hung a spring in it, the end of the spring was outside the rear quarter !!

I would for sure set it down on the tires before you weld the perches on. I measured mine off the rails and and one tire hit the leaf springs, thankfully I hadn't welded it all up yet.

I got real scientific with it, my clearance was limited so I put the tires on and I have one crescent wrench handle between the sidewall and leaf springs on each side. This distance works well and nothing rubs, I have zero room to move either direction really. If you use this method make sure to use a standard crescent wrench and not a metric one!

My son's 68 Dart 270's 7 1/4 looked good with the steel wheels and 165/70 14's. Put the A body 8 3/4 in with 15 inch Cop car ralley's and 235/60 15's and it still looked 'KIND OF' ok but you could see the right tire was closer to the fender.
Fast forward a couple years. We put in the spring hanger kit inside the frame. Added new spring perches exactly the same distance inboard from the old ones, leaving the old ones in place. Put some Foose wheels with 325/50 20's under and the right side tire has 3/8" clearance but the left side has 13/16" gap. Just 7/16 difference. So I used some string and cross Diag'ed the frame and it is not square by any means.

most mopars driveshaft is off set to pass side, measure trans output shaft centerline framerail to framerail, put center of pinion same place. axle flanges will be were it ends up (non adjustable) set pinion angle with weight on ground then tack

gary