WWII vintage rifles would still have been in service when your father was in the Reserves and I would assume new production rifles (1950s) would have gone to Regular units first so while you can't be certain, it's a safer bet that he used a wartime production rifle.
1. Yes
2. Long Branch armed British and Commonwealth troops.
3. No
4. Yes
Long Branch and Savage supplied many No.4 rifles to British and Commonwealth forces during the war and Long Branch rifles were supplied to allies after the war. Canadian troops started out with existing stocks of No1.Mk3 (all British-made, procured during and after WWI to replace the Ross, Canada never manufactured the No.1 rifle.) The first Canadian troops in England would have eventually got No.4 rifles to replace the No. 1 through integrated supply. Priority of issue would be to British troops that lost weapons when evacuated at Dunkirk and new British units raised in Britain. Canadian units would have arrived in Britain with good serviceable rifles (the old No.1 initially, then Long Branch No.4) issued to them in Canada and brought with them.
I believe the Canadians fighting in the Mediterranean theatre started out with the No.1 rifle and I don't know when they got the No.4 rifle. 8th Army fought their Desert war with the No.1 rifle and changing the whole lot over to a different rifle would complicate logistics enough that it would not have been done without some careful thought about the timing. When Canadian troops got No. 4 rifles they probably usually got Canadian rifles but as things go in war, operating integrated under British command (and with British units sometimes part of Canadian formations e.g. 21 Army Group in north west Europe was a British command which included a Canadian Army which included a British Corps at times) they certainly would have been supplied with British-built rifles sometimes.
Long Branch initially made the No.4Mark1 design then introduced a variant that was easier to manufacture. It did it away with the spring loaded catch behind the charger bridge which released the bolt head from the guide slot in the receiver so it can rotate up to clear the rear sight when removing the bolt. This version is No.4Mark1*, the Savage factory also adopted this modified design, none of the British factories did. Any rifle that was in U.K., including Canadian Army rifles could have been sent for FTR and as far as I know only Royal Ordnance Factory Fazackerley did FTR, they certainly did most. They were marked FTR. When the new design No.4Mk2 (introduced post WWII, Long Branch never made this one) with its trigger hung from the receiver instead of the trigger guard entered service the FTR process included modifying the trigger attachment on Mk1 and Mk1* rifles to attach on the receiver (not exactly like the Mk.2 because those receivers were made for it, the older design was a modification, but still it's better than attaching on the trigger guard.) When a rifle went through FTR and got this trigger modification it was marked FTR and re-designated: No.4Mk1 became No.4Mk1/2 and No.4Mk1* became No.4Mk1/3.
Get a Long Branch No.4Mk1* because it's Canadian and the most likely type to have been in your father's hands, get one with an early production date because it's most likely to have seen combat or at least war service, or a Long Branch No.4Mk1 for the same reason plus it's less common than Mk1* so a bit more valuable, a No.4Mk1/3 because it's the right type plus it's got the improved trigger attachment, or get a post WWII Long Branch rifle because your father may have used one of these newer ones (and it may have been used in combat in Korea.)
