what do they mean???

It depends on "where" this stamping comes from.

The most important information on a block is usually cast,...like 360-3, calender date, 1975 (ect), night/day shift.

The numbers you have sound like they are coming from below the drivers side head in front, and I would guess they have to do with the vehicle your 360 was originally installed in....the last numbers sound exactly like a production number which would coorespond to a VIN...the rest I cannot help you with....hope that helps.