I know '40 axles have been used under Model-A frames and the wishbone can be split, but isn't the spring in front of the axle? I guess you could get spring-over-the-axle perches and saw off the spring mounts, but for $300 you could buy a Econo disk brake kit for your existing axle. If you only want the backing plates and brake parts that price is too high compared to several modern disk brake kits. I guess you would get split wishbones and backing plates compared to an econo disk kit and hairpin or four-bar. Unless you are extremely into retro building it looks like you are spending more to get a setup that has been improved on since 1950.

Don Shillady
Retired Scientist/teen rodder