If it was a drum conversion then it wasn't the Browning design. That used the original tubular magazine. There was a device (paddle for lack of a better term) on the end of the barrel, connected by a swinging link. This "paddle" was connected by linkage to the lever, which then operated the action. Thus FA fire was effected.
The conversion you're talking about sounds intruiqing. Have you tried asking on Big Jim's Machinegun Sanctuary?
Www.bigjimsmgs.com.