The first picture is of the old subframe connectors under the car. The second picture is of the regtangular tubing I will be using compared to the size of the old subframe connector. The tubing is 48" x 3" x 1 1/2". The connectors are exaclty 4ft long. What I did was go downtown and purchase an 8ft section from a welding shop and had them cut it in half. I think it cost about 35 bucks. The third picure is of the finished driver side subframe connector.

The first picture is of the first cut I made to fit the floor support under the driver's floor pan. Notice the connector doesn't sit directly under the rear unibody frame, but off to the side. I wanted to keep the connectors directly parallel to the rockers. After a good fit I was ready to move on.

This is the second cut I had to make to the subframe connector. Notice the reason for this is that the rear floor pan comes down and gets in the way of the connector. All I had to remove was 1/2 an inch. The rectangular tube is 1 1/2 inch in height by 3 inches wide leaving.

Making sure the subframe connector is level is important. I'm also going to use the piece I cut out to as a cover plate to fill in the hole, but first I have to trim it and make it flat.

After adding shims for the cover plate and prepping the inside I was ready to clamp the cover plate on. I had to enlarge the cut by about an inch and a half but it was not a very big deal,  just did the same thing for that small segment and finished things off by adding caps to fill in the ends.

After laying down a weld bead all the way around, I ground down the welds. If you look closely at the right side in the first pic you will see a hole right above where the end caps were welded.

The subframe connector was just barely rubbing up against the frame in this area and needed to be adjusted. All I could do is cut out a wedge and weld it back in. I used a magnet to hold a piece of metal in place and then just welded it all together and ground down the welds. (This is actually the passenger side unit, but I had to make this cut on both connectors).

Time for the subframe connector to get fit again and measuring for the brackets that will weld to the frame.

Sometimes the welding doesn't come out exactly the way you thought it would but it's good enough. The inside wall of the floor support in the first pic has been reinforced with 16ga metal so the top of the subframe connector isn't just welded ot the thinner metal of the floor support. Along with the bottom welded to the steel L beam, it's not going anywhere.

All done! Hope my project helps you out in adding subframe connectors to your classic mustang and if you think you can improve on my design do it and send me a pic! I'll add it to the website!