My 71 seats suffer from the common C3 seat malady: broken/sagging seat tops/back & bottoms. I had a small pillow wedged behind the seat because the rake was too extreme and never lined up correctly.

This is due to the extreme pressure and angles of the back seat bolts hammering down into the bottom seat area. My upper bolts were bent completely and never lined up with the bottoms. Also, the bottom bolts had either been punched out (each square nut is tiny spot welded in place and easily it "punched" out with the weight from above.

I had seen a metal plate you can bolt into the seat bottom to spread out the weight over the entire seat bottom but also realign the bolt holes, bolts, and bumper stoppers.  

My main concern was whether I'd have to peel back the leather covers; more like how much disassembly would it require to repair them.

Obviously I didn't want to completely tear them down, because then you might as well start from scratch with new covers. My original leather seats look fine (not mint) but have many years left in them.

Bought the plates, and installed one last night. It was fairly easy. I did one seat and it took about 1-1/2 hours to do it, with most of the time hunting down some extra "reinforcement" nuts and washers (one I had to grind and edge off).

Follow along with these pics.

The leather cover is just clipped over the edges (backed by a thick cardboard-ish material). Just pry up slowly on the clips to free them. The front clips and a few on the sides just around the corners is all that is needed.

Take all 4 "bolts" out:

The outer 2 seat bottom "stoppers" unscrew with a phillips screwdriver. 

The 2 inner longer pointed bolts hold the seat back metal strip - it basically holds and limits the seat back from tilting forward only so far. 

Now you have complete access to slip in the metal plate. Just sandwich it in until the new plates holes line up fairly well. I had a hard time lining both at the same time. So do the insides first, to align the plate where it supposed to be.  

Just to hold it in there to be able to work in the outer bolts.

My seat bottom's frame was tweaked, even having a crack and folded metal from where the square OEM nut is tacked down. You can use the stock bolts (longer ones would help), but the object is to pull the metal back in shape- slowly. So thread in the bolts and once it pokes through the bottom, try to get a nut and a washer on it.

The threads aren't that long, so start first with just the nut. Make sure the bumpers are threaded almost all the way and hold them from rotating with a Phillips screwdriver while the bottom nut is tightened. You're basically flattening out the ragged metal under there. Eventually you'll be able to stack a few washers under the the nut, reinforcing the deal by pulling the metal plate and frame completely together.  

Do both outers a little at a time so it pulls down evenly. About a quarter way through the outers being started, reattach the seat back metal strap with the 2 inner bolts. As those tighten, it'll all begin to "smooth" out the bottom frame.

On one outer side, I couldn't use a full washer because it was to tight a fit. The pic shows a screwdriver gently prying up the bolt to reposition the metal plate just slightly. Then I ground down one end of a few washers to stack under the nut. 

If i wanted to, I could also put some nuts under the inner brace bolts, too, but I deemed it unnecessary.

After that, I used a pliers to re-crimp or squeeze the leather cover clips closed- so when I would slid them back down, it was stay tight like before.

Now, I have to buy new seat back bolts to reposition my "like-new" original deluxe seats. I had bought longer, very close bolts with slightly different heads, but I'm just going to by some stockers.  

One, the seat tracks are bolted on by 2 bolts, each on opposite ends. The one side with the slider handle, you need to unscrew the ball lever, then move it into position so the bolts are exposed. Pull the lever through the "slit" by rotating it slightly and it'll clear out. Simple deal here.