Frame rail replacement on a '68

[MoparMan]

I have a '68 charger with the original 383, 727 and 8 3/4. This car is very complete and actually runs and drives. My biggest problem is that the car is very rusty. I believe that it will need both rear frame rails replaced along with the trunk pan and most of the floor and quarter panels. I think I can handle the sheet metal but the frame rails are very intimidating. Has anyone else done these before??? How do I get everything lined up right and what is the best way to start. Several people have suggested that I part the car out but I could never do that. Any help would be appreciated!

[SFRT]

I replaced a full front rail....

1. get the car totally stable and as 'square' as you can. I used 10 jackstands, 2 carjacks, a million big c clamps.. a ton of wooden blocks and a couple of big 6' aluminum levels plus a magnetic torpedo level...
2. temporarily tack weld some tubing from the most solid part of the car to whatever area might 'move'
3. measure everything like 50 times. cut the old rail where it butts into a crossmember.follow the original weld lines they are like a map for you. take the cut piece and compare it to your replacement piece.
measure everything again.

4.totally clean all surface to bright shiny metal.

5. using more jackstands and blocks and clamps position you replacement rail. measure everything again and again.

6.now...imagine your trunk area as a square....pick 4 points that are at the corners, for your diagonal measurement. get a rod and attach 2 pointers to it ( they actually sell a tool) that reaches acorss the diagonal...

7.measure everything again.

8. tack weld the new piece on.

9, use your rode to determikne how close you are...wack it alittle with a hammer.....more tack welds to draw it the other way...repeat...

eventually you will be really close...then run the beads. you can be like 1/32-1/16th off it wont matter in the long run.

I spent like 8 hours measuring and prepping then 30 minutes welding and hammering and it came out fine.

if you mess up. cut grind out the weld and start over.

[SFRT]

oh yeah get 2 guys that are really patient to hold stuff while you measure everything 5000 times.

[Mike DC]

You might wanna swap the entire rear end of the floor/subframe as one big lump if both rails are wasted.  There's a bunch of threads on this job already.

Any '66-70 B-body (even the 4drs) have the same subframe rail structure as the '68-70 Chargers.  You can still find/buy decent used rear subframe clips for pretty tolerable prices, compared to doing it one piece at a time with reproduction items.