According to my copy of Old Rifle Scopes by Nick Stroebel, the G series were rimfire scopes, introduced in 1947. They were replaced by the B4 and B6 in 1954, which in turn were replaced by the C series rimfire scopes, with larger ocular and objective lenses, in 1966, and these were replaced by the D series (on a 7/8" tube) in 1970.
The J2.5X and J4X were advertised as scopes for high-powered rifles, and were introduced in 1947 to replace the 330 and 440. They were dropped in 1967 and replaced by the A2.8 and A4, both of which were dropped in 1969.
It is worth noting that the 1" tube K series scopes were contemporaneous with these, being introduced in 1947, though updated at various times since.
Stroebel's book has some more detail, including dimensions, weights, FOV, and eye relief for a range of these. It is well worth getting if you can find a copy.