Spring
Chopper lumps are really the only system where the lumps are actually integral with the barrels.
All other methods require that the lumps are welded to the barrels.
Monoblock, dovetail, and shoe-lumps, are all attached to the barrels by some sort of weld.

Regarding extended top tangs.
These do NOTHING toward strengthening the stock where recoil from big NE cartridges are concerned.
They do however provide some assistance to the grip area of the stock when the gun is being broken.
They do this by taking some of the load that the breech pin/ hole endures as the gun is opened.
Extended top straps do look great but IMO they have NO place on a boxlock double which is to be used in hunting conditions.
On sidelocks and droplocks where the lock mechanism is easily removed extended tangs are fine.
Boxlocks however, are not easy to field strip for most owners, if the gun gets rained on, and if a boxlock has an extended top tang the field strip job becomes even more difficult.