My 725 seat springs were looking tired and both plywood seat bases were cracked at the corners where the brackets attach - so I decided to start over with them. I traced and cut new plywood bases out of 3/4" MDO plywood and ordered the high density foam seat bottoms and back rests from OD Cloth.

And semi public service announcement here: I experimented with some NOS M715 seat covers and I tried to wash and scrub them to remove the really stinky canvas waterproofing that rubbed off brown oil on everything. . . The washing removed some of the oily residue, but . . . . . . yes, they shrunk, like a lot . . . . . so that was a total fail as was my attempt to stretch them out again. After that attempt failed, I also ended up getting a set of the OD Cloth M715 seat covers, which are beautiful and well made with Donna's attention to detail and they now the seats make everything else about my truck look ratty.

The seat foam is surprisingly firm and matches the seat base and a back rest shapes really closely. And the seats now feel much more comfortable than before with the springs. I still need to lace up my seat covers and attach the seat bottom corner brackets to the plywood.
Note: I also have the two old seat bases/springs up for grabs if you want them for the price of shipping. One has a stapled on cover the other set is bare springs. See pics with one of the old seats below. Let me know if you want them.

I did a couple of things differently with my seats:

Using spray foam adhesive, I adhered a 1" layer of outdoor polyester upholstery batting (NuFoam from Fabric Depot) to five sides of the seat bottoms and back rest foams. This material fills out the seat cover a little more, softens the seat somewhat and protects the foam rubber from abrasion from seams of the fabric cover. Also the backrest foam felt a little thin and the batting helps make it so you can't feel the metal backrest frame as much.

I also came up with an easy way to address the bent and mangled seat back sheet metal/multiple broken spot welds by fitting and TIG welding in two 3/4" square tube supports for each seat back and TIG spot welding the sheet metal back onto the frames and new tubing. I suppose that the seat backs can now be walked on without bending.
I posted some photos over in photobucket . . . . Oh, well . . . It looks like I'm gonna have to figure out that process later. . . . I looked for an "easy" button for photo attaching here and only found the button labeled "frustrating". My luck I guess.

Cheers,
Brycer1968