I may be able to help you with this.
That was the main problem with my 69. My windshield frame upper was in great shape, the lower was fair, and the rockers were shot.
I call them rocker supports, or body frame rails, but in any event they go from A pillar (hinge post) to B pillar (lock post) under the sill plate and fiberglass.
Okay, here is the good and bad. Paragon sells a repair kit which is a channel that will slip into the original from the bottom and gets sleeved and welded into the pillars. Obviously, the body has to come off the frame. The bad part to this is most of the old rusty channel stays up in the car and will continue to rust and possibly infect the new metal you install. I actually bought these and welded them in solid in place of the original. It was tricky because I had to make up the space that the original channel took so that it would all fit.
There is another option. I have a good set of rockers out of a 71 that are in decent shape. As long as your A and B pillars are okay, you should be able to cut back the glass, drill out the rivets, and weld in a replacement set. Prices vary for these. Like I said, I have a set sitting around. I can send you pics, etc. Don't know what is involved in shipping, but I could let you have them for $100.
However, if your lower A and B pillars are rotted out as well, You have very little choice but to cut the whole body frame out and seek a replacement. I believe you saw my thread about how I get my hookers for free (side pipes). I have some great pics of there of how you will actually re-bond the body frame to the body.
If I can do it (twice now) anybody can.
