If you can provide the Serial Number of the machine, from the placard on the electrical door (with that age machine it was either outside, or inside)
Doosan has most manuals still available, for Doosan, Daewoo, and Mechatech machines.
Most of them are less than 100 dollars (US) each...(around 300 for the entire set that shipped with the machine. (Safety, Instruction, Operation, Parts, and Electrical)
Note: These are not FANUC Manuals. (You would get those from Fanuc)