Yep, return springs always go behind the brake shoes to pull them back against the steadying posts on the backing plate.
Incidently, there are little white felt bushes on these posts, and if they are missing, this can cause the shoes to set up a rattle that is very hard to pin down.
Both 9" and 10" drums are interchangeable between Lockheed and Girling brakes. For what (little) it's worth, I believe the drum manufacturer for the factory was Qualcast, a UK company that made lawnmowers.
Regarding the query on the TR3B Commission plate, mine just had TCF2650L, being the 154th last sidescreen car made. The body number on the firewall also had a TCF prefix. Like the 3A's, there was no special factory recognition....apparently they were all just known as TR3's.
Viv.
Incidently, a snippet on 3B's passed on years ago by a retired factory engineer who lived nearby, was the TCF second series was so called being obviously "T" for Triumph, "C" being a commission number used on TR4's, to denote that all these later 3B's had TR4 engines, gearboxes and front brakes. "F" was for the Forward Radiator company, an S-T subsidiary, where the 3B's were made.