The earlier version of the 760 had the Bolt Carrier brazed to the Action Bars.
They were neatly induction brazed so the braze joint isn't normally easy to see.
The actual Bolt (head) itself and all the related small parts (firing pin, ejector, extractor, cam pins, ect dismount from the Bolt Carrier for maint, cleaning and repair.
Sometime in 1952 ,,so shortly after production started (1951/52), is when I believe Remington changed over to the simpler system of having the Bolt Carrier itself just held in place by the shape of the over arch of the action bar.
These 'old style' action bars may have still been in stock and used on later assembled rifles as nothing was wasted.
I don't have a ser# for the change over , sorry.
Added..
The ser#'s for the 760 started w/# 1000
I'd guess a rifle in the 51,000 range was built in the 1952 era.
A better idea is to check the Remington Bbl Date Code on the side of the bbl at the breech.
It will give you a month/yr the gun was proofed at Remington.
Tht will be the code closest to the frame.
Going out towards the muzzle there may be additional date codes usualy with a '3' added. Those are 'Repair' codes,,Returned to Remington Repair dates.
Here's a list of the date codes.
Manufacture Dates – Remington Society of America
