what I have learned till now is this project startet maybe in 1946/47. the idea behind this was to made a low budget hunting rifle for hunters who lost the rifle in WW 2 because of gun confiscation.
oldest date I have is 1947, last rifle build by Mas proably 1950/51.
it seems they made 2000 - 2500 actions with serial number in the white + stocks and offer the rifle in 7x57, 8x60S and 10,75x68. maybe barrels where also made in small lots before.
whenever they get an order for a rifle one action was taken and a barrel in the desired caliber was screwed in. the actions probably rest in a big box and they taken the one above not looking number 2 came after number 1 any time.
in 1950/51 french firms find out that MAS as a state owned arsenal was not allowed to made hunting guns for the market and so they made trouble about it.
MAS abandon the thing but the man in charge of this project Jean Fournier decided to work as a private master gunmaker now on his own. he leave the firm bought the rest of the parts still on stock and continue to offer hunting rifles now made in his own shop. probably the same time the 7x57 Mauser became again illegal for civil use like it was before but only in the mainland and not in the colonys.
Fournier solving the problem by create his own wildcat the 7x54 Fournier, a 7,5x54 necked down to 7 mm with 7x57 ballistic. the chamber reamer of the 7x54 was enough to rechamber the old 7x57 barrels he still had.
so you see older MAS made 7x57 rifles rechambered for the 7x54, rifles made from the original stock build by Fournier with the original MAS serial number. sometimes the actions had no caliber designation before or the old 7x57 designation was xed out or overwritten, changed into a "7x54".
such rifles have sometimes an extra "JF xxx" serial number and sometimes not.

https://www.pressreader.com/france/armes-de-chasse/20160101/282514362462591

after the old stock ended Fournier was buying MAS 36 parts from MAS and continued to made rifles now having only the 7x54 designation on the action and his own JF serial number.