Colt 601 Build

[browningautorifle]

You must mean the hole offset in the end of receiver where the detent spring inserts, and protrudes out then just rides flush against the end of the stock

That's right.

thought there was a shallow hole on the later stocks that helped to index and hold that detent spring

Nope, they just sit flush. Inexperienced people sometimes damage the spring by pinching it while rotating the stock.