Given it's age, it probably needs the old Shimano splined remover. This is similar in shape to the current version, though with a smaller diameter.

Shimano enlarged the removal spline diameter some time in the eighties, so that a thin walled remover could be slid over the axle. On yours, you'll need to remove either the axle lock nut and right hand spacers (often there will be an second locknut deeper inside so the bearings won't need readjusting. If you cannot remover enough spacers on the right, you'll need to disassemble the axle from the left side and slide it out.

BTW- if you're planning or replacing the freewheel, let a bike shop do it since it should cost $5.00 or so (bring only the wheel), which is less than the remover. Otherwise if you need to buy the remover, I might have one to sell and it would be less than what you see in the link. Only problem is I won't know for sure until I go to work on Monday.