It's not GM, but I saw a very nice 47 this past summer at the Street Rods Nats in Burlington, Vt. from Canada where the owner had used the entire suspension from an 86 Chrysler 5th Avenue. The suspension was the correct width and the truck had a nice stance. He even used the COP dog dish hubcaps on the Chrysler wheels. That model Chrysler uses a torsion bar suspension and ride height can be set without experimenting with various coil springs. He was pulling a travel trailer with the truck and had logged about 25K miles on it with no problems. He used the 318 and automatic from the Chrysler, steering column, power brake master cylinder, and rear end including the rear springs. He said he even used the Chrysler driveshaft and didn't have to modify it. I believe your frame is the same width as a 48-52, and if so, you can use the video available from No-Limit Engineering (for 53-55s) to install the T-bar suspension. You do not have to cut off your frame like you would with a GM subframe as only a notch is necessary. I'm installing this same suspension into my 48 F-3 but using a GM engine and transmission. The notching results in less fabrication to reinstall the core support and front sheetmetal although I've found that a little more trimming here and there is necessary than on the 53-55 installation.
If it must be GM, I'd look for an early Camaro (67-69) or Nova (68-73) which has the rear steer subframe. The Nova clones like Pontiac Ventura, Olds Omega, and Buick Apollo between 68-73 also have the rear steer subframes. These subframes are four inches narrower than the later front steer subframes.
