Try Brownells for the loop. I think that a '94 large lever loop cut off and welded to a '73 lever base would probably work well. I installed a large loop on my '94, looks great, fun to shoot, and as stated above- slow as molasses.
NRA, VCDL, USAF 1970-76 6200FMS CLARK FIELD,P.I.'71-'72- 18 SOS, NKP, THAILAND '72, BASE FLIGHT,KEESLER AFB,MISS '72-'74, CARSWELL AFB,TX '74-'76