Those are Cadillac/Olds FWD rear calipers. TSM even calls them "Small GM Rear". I doubt they would be an upgrade in braking power.... maybe weight?
http://www.tsmmfg.com/More.../3110.html
You got to dig a little deeper into their website, and their are a couple of mistakes in it.
The caliper you referenced, the #3110, is the small one with a 2 1/32 piston.
You can get the larger caliper, #3120, which has a 2 13/32 piston, a big difference in swept area.
Its just that the website miss-identified it as a front caliper.
I know, I put one of their kits on an 8,600 gvw square body with a FF 14 bolt, that regularly carried heavy loads, and the stopping ability was much better than the factory disc/drum set-up,,.
However, I agree, that if someone can get an 800 axle for cheap, and change the mounting scheme, than that is a good way to go.