The period correct B&L bases use the plunger tube solid rings for the straight tube 2X,4x or variable 2 1/2-4 Balvar.Rear base uses the receiver sight holes on the rear ring;front base uses factory holes on front receiver ring.There were no top holes on the rear receiver ring. You may be able to use later plunger tube split rings with the large objective Balvar 8 but it may not clear the bbl.
