firstly I am not baggin Boling Bros products ..... they are a great product and I'd happily buy from them again. I've just finished my roadster which uses their front and rear 37 - 48 brake kit and drums. The rears are working fine, however on heavy braking the rear shoe on both front brakes moves out and touches the drum, leaving a score mark. Has anyone had this happen to them. Any suggestions?
Check that the area of the backing plates where the back of the brake shoes ride is not warped. Put a dial indicator on a spare hub with the plunger on the flange of the backing plate and turn the hub. That will probably tell you something. The set that I put on the front of my '40 did the same thing as yours. I put a LARGE Crescent wrench on the backing plates and tweaked them enough to get rid of most of the warpage, no more issues with scoring the drums. When I installed the next set on the front of my roadster I checked and straightened them before putting them on. Didn't have any issues with them...
I have seen hubs cut a little coarse that acted like a screw walking the shoes out. Probably not on new stuff from Bolings though.
Look at @33Doll build thread. He had a maybe similar problem and added an extra hold down pin and spring to stop it. He posted pictures too.