A few responses:
No, I was not referring to the Vickers K or VGO when I mentioned that some Vickers guns were adapted to take a Lewis-type drum. The VGO's drum was entirely different, being powered by a spring (as most others were) rather than by the gun mechanism (as the Lewis drum was). What I was talking about is covered in the second volume of Flying Guns: Development of Aircraft Guns, Ammunition and Installations
, which covers the period from 1933-1945. Vickers produced new versions of the Vickers-Maxim type action in the Class E (belt-fed, for fixed mounting) and Class F (with the 97-round Lewis drum, for flexible mounting). It was sold only for export to various countries (including Japan, Greece and Poland) and did not see RAF service.
The Hazleton Adapter, as fitted to the Vickers, was a gas-trap device fitted to the muzzle which kicked the barrel back more quickly to increase the rate of fire. It is generally known as a "muzzle booster" or "recoil intensifier" and was later commonly built in to recoil-operated MGs from the start. This device could never have been fitted to the Lewis, which used gas operation with a fixed barrel - there is simply no way that it could possibly have worked. Something different must have been done to speed up the Lewis, although I'm not sure what. The standard method of speeding up gas-operated guns is to enlarge the gas port, allowing more gas to hit the piston which operates the mechanism which kicks it back with more force. Another possible way (which could be in combination with the first one) is to lighten the bolt and weaken the mainspring, but put a strong buffer spring at the rear to kick the bolt back more violently. All of these approaches will indeed put severe stress on the gun and will cause increased wear and probably breakages, if the vulnerable parts are not strengthened. The VGO was an aircraft version of the Vickers-Berthier LMG, speeded up from c.550 to 950 rpm, and that had to be significantly strengthened.
Guns designed to use either belt or magazine feed generally fire faster with the magazines: belt drag is a distinct handicap.