To add a bit to Rogers photo essay and a bit more info on the repro base.
The repro base does fit the commercial G & H rings well, but is sloppy as "H" on the No.67 rings.
Bottom unit is an early G & H set of rings (possible trials use) and top unit is a set of original (as yet unassembled) 67 rings. Base is unknown and I have no documentation other than it came with the top end when I got it many years ago.
The early trials with the No.67 and the 32TPscopes used commercial mounts with scopes manufactured by REL at Leaside (Toronto) or Montreal and Lyman in the USAwith the Alaskan. Mounts were made by S.A.L. (Small Arms Limited) according to records as well as commercial G & H mounts.
Records are very scarce on REL and S.A.L. therefore most of the info known is first hand from those involved at the time.
SO...bottom line on the repro base is it will fit the commercial G & H rings and was destined to be used on the No.4 to make up "a look alike sniper" however the back of the mount is not machined correctly.
I also forgot the Weaver 330 that was used during the trials but it was used on a Springfield rifle but does deserve honourable mention.