"Could a later one drop in?"
I don't see why you couldn't. There are no differences between a 1916 production receiver and a 1918 (800000+ serial#) receiver that I can find in any references such as Brophy etc. As too minor dimensional differences between two such actions, you may not know until you have the replacement in hand. Have the bluing matched and you would supposedly have a safe for modern high pressure ammunition Springfield. Since I don't own a Griffin rifle, someone else will have to address if he made any alterations to the receiver itself.
Would it degrade the rifle? IMHO yes, but then who would know 10 years from now? I just can't see or justify doing it in my mind. But if someone wanted to spend the $ for it and do it, who am I or we to say what they can do with their possession.
Thaine
