I wouldn’t consider that shoe lump construction, of which I’ve never seen fail. It’s good enough for Westley Richard’s to use for their double rifles, as well as Heym.
As I understand it, platform lump and shoe lump are the same basic type, with some differing a bit in the amount of "purchase" the brazing has to work with. They differ from almost all other methods in that they have no mechanical joining but are totally dependent on the brazing/soldering to stay together.
This is the only available description, with drawings, that I am aware of.
https://www.hallowellco.com/lumps.htm In the drawing on Hallowell's site, for shoe lump construction, you can see the additional area for braze, as compared to the amount of area in the pic of the Parker Repro above.
