... and the rear brake bridge.
Are screws better in tension of shear?
I think you want something that is held together by the screws but I'm not sure you want the screw to be the primary load path. How about a stay that fits well and is bolted in place such that the end fittings transfer the loads directly to the frame and do not go through the bolt. Normally, a stay is under compressive loading, correct? That way the screw only has to hold the stay in place so it can do its job. Ditto for tensile loading (if possible).
Don't know except the bolt up stays were on all the roadsters I've seen with full chaincases. Most are well over 50 years old and still on the road, so I guess it works just fine.
IMHO much better than that cut and braze job in the video. Kinda made a simple application a difficult task. If we ignore history we are destined to repeat it!