That stud with the hex bolt in the end was how these were charged back in the day.
You needed a special access tool which we all carried, however these days you could cut into the suction line or fit an access port on the suction line.
You will have to check on the compatibility of the refrigerant you are going to recharge this with as it would have been originally charged with R12.
Those compressors were so reliable, they were used on small fractional HP commercial condensing units in addition to domestic refrigerators and freezer cabinets.
Long before there were specialist vacuum pumps available we were issued with these compressors mounted on a tubular frame as Vacuum pumps.
How things have changed, not always for the better in some ways.

Best of luck with the project.