Help! I think I need a frame Jig.

[Cncguy]

Working on my charger this weekend, I found evidence that the previous owner may have swapped out the rear frame rails at some point. Im not sure I can trust their current locations. Is there a way I can check? If not , I'm hopeing someone on here can get me plans for building a frame jig.

[areibel]

If you have a factory manual it has the the locations and dimensions to measure it yourself, I can't remember but I think if they're within a quarter of an inch of the spec you're OK.  And someone may have even posted a copy of that pic here somewhere if my foggy memory is correct.  I don't think you'd need a jig unless you have to move something.
Al

[FJMG]

While I firmly believe in a frame jig, like mentioned above, you may want to start by looking at the factory service manual drawing and dropping plumb bobs (remember those) from the measuring points shown on the drawing and making marks on a flat floor and compare those dimensions to factory.
From there you can determine need for a jig.

[Cncguy]

Ok Thanks guys. I found this drawing online, do I use these measurements to build a jig, the datum representing the floor of the jig?

[areibel]

That should be what you need.  To check it out you could just do as FJMG suggested with a plumb bob.  If you have a decent concrete slab mark the hole location (centers)  on the floor with the plumb bob and chalk, then roll the car out of the way and check to see if everything is kosher.  If it isn't, that's when you need to build a jig.  I've seen replaced frame rails that dropped right into place and lined up perfectly, and I've seen the results of some hillbilly engineering that didn't go so well!  You can't tell until you measure though.
I used to have piece of 1/2 by 1/8 steel that was about 4 inches long, you could fish it up into the hole and get your string centered, then you can just hang the bob and start marking.