The two groove barrels most Savage rifles were fitted with didn't make the No.4T conversion specification hence the change to a five groove barrel. Early Savage Mk.1 rifles retained the six groove barrel. I think some two groove barrels also slipped through the conversion process too so nothing is written in stone. The forends will interchange with no problem regardless of who made the barrel. I'd guess that British made replacements were used when the existing forend wouldn't meet the conversion standard for whatever reason. As for the Savage made Mk.1 rear sights, I think many were supplied as spares to both Englandand Canada
. They can be found as modified on Long Branch conversions also.
I had 400 or so of the South African War Reserve No.4's as imported by Interarms in the early to mid 1990's. There were quite a few Savage rifles, (probably 50 or 60 give or take), and a very few Long Branch in the mix which was mostly post war Fazakerley production; Mk.1, 1/2 conversions, and some early Mk.2. Some of the Savage rifles were in new condition other than handling marks in the woodwork. I found 10 or 12 early Mk.1 Savage rifles, one 5Cxxxx that I still have in original condition. All of the Savage rifles were dated '41 and '42. I don't recall seeing any dated '43 or the later undated '44 production rifles.