I have a 1976 Boler 1300 made at the same factory. Its' serial number is 360072 (model 130-A-S).
There is an oval sticker to the left of the door (on the outside) that has the date on it. I think this may be the date it was sold
(March 1976) as another sticker next to the fridge
vent shows 11/75 which is likely the actual build date.
If your stickers are missing or illegible I don't know where else you can find the date. You may have to estimate it based on other serial numbers that are close to yours.
Also, is there a Boler emblem above the front & rear windows
or a decal below the window? I think 1974 or 75 was the last year that had emblems, in 1976 they used decals.