I just finished putting 4th gen seats and Morris 3-point seatbelts in my 67, and I'm stoked on how they came out so figured I'd share...
I bought a pair of manual seats from a 97 Camaro, and another driver side seat track from a similar year Firebird. The driver side track is easier to modify to make it work. It would be difficult to get the level and angle of the passenger seat to match with the passenger track, plus you get manual tilt on both sides. I also found this awesome tool
, which I've needed for years for various projects, but didn't know existed.
With the tracks off the seats, I cleaned them up, and ground off the rivets holding the rear mount brackets to the tracks to completely remove them. I then reinstalled the tracks on the seats, put them back in the car, and bolted the front mounts down (they line up perfectly). I used some small pieces of cardboard to determine roughly what the new brackets would look like, and found that 1 1/4" wide flat stock would do the trick. I bought a stick of 1/8" thick x 1 1/4" carbon steel from Home Depot.
The brackets I made provide about 7/8" rise in the Z bends, mainly because that was the minimum I could do with the vise brake. The other dimensions are up to you, but the throat of the vise brake limits the bend on the floor to about 3/4" in order to have clearance to make the second bend. I have a drawing of the bracket blanks, but I can't pull it up right now. Will post later if someone needs them.
I cut and bent blank brackets with only the hole for the floor bolts at first. I have a drawing, but can't pull it up right now. I can post it later if needed, but it's pretty straightforward. I then installed the new brackets under the tracks in the car, squared up the tracks (they will move a bit, and you need to make sure the slide lock works without binding). I marked where to drill the holes to bolt them to the tracks. Took the brackets back out, drilled the match holes, and installed them on the tracks with 1/4"-20 x 5/8" machine screws with locknuts.
I also installed Morris 3-point belts, and the new seats just clear the recoil mechanisms by the rocker panels. No trimming needed anywhere!
Here are some pics. Hope this helps someone out!