I have never seen a drilling jig for an 1891 Argentine Mauser... I've seen them for the K98/large ring. Also I've seen the cost for said drilling jigs... And not being a gunsmith it's hard to justify buying a hundred dollar jig for one receiver, one time...
I wouldn't be tackling this ordeal with a 18v Milwaukee or anything like that. I have access to a drill press I would use if I knew exact hole placement for the mounts.
When I die better bury me deep, two .45s layin' at my feet,
An M16 across my chest, tell Chesty Puller I did my best