I was relying mostly on the crossbolt type and not on the chatter. However, the mill marks between the Kokura and the SLD are nearly identical in several places... if I could show them side by side in person (can't really capture the dimension/depth with my camera), you would see what I meant.
The seller has been following the thread and offered a full refund after seeing the other examples here; I wasn't really worried about that as he is unequivocally a stand-up guy and didn't do anything to this rifle after buying it years ago. It looks on initial examination to be consistent with Jinsen stocks so he didn't "dig". It was among the best cared for (oiled and preserved) and packed rifles I have ever purchased.
What threw me immediately was the crossbolt style. Every late Jinsen I have ever seen or owned had slotted washers on both sides with a peened crosspiece. Since there is a comment that I might not be right (I would love to have folks tell me "mine is just like that with great Jinsen inspection proofs, stop worrying doofus") I took the rifle the rest of the way down this AM looking anywhere on the stock or fittings for Jinsen-related proofs. (the bands and all metal parts that should be SLD characteristic are). I wanted to see a Jinsen proof that would make this correct; these things are hard to find for sale and it is on my short list!!!
The rear sling swivel (underneath) and the inside of the handguard channel ARE proofed... flattened "M" and "ij" (Torimatsu). Interesting because there is no way this is a Nagoya stock? No inner proofs or markings anywhere on the stock itself (the Nagoyas I have seen are normally proofed).
For final consideration, there is a small "blip" in rifles near this SN range in the Type 99 book showing this type of stock (Type "C" no fullers, separate forestock) in the 84-87k range in the midst of Type Bs (fullers, solid) and a couple of F's (fullers, trapped forestock). A small shipment of Kokura stocks? Would Kokura also have shipped some Nagoya proofed small parts?
I am working with the seller on what I decide to do. I am not likely to find one with the metal like this again, but the mix of stock parts seems to indicate that it has been re-stocked at some point a LONG time ago with parts from other guns.
What do you guys think? Should I hang on to it and just look for a mismatched, ground late Jinsen to provide a donor stock down the road??
Again, the seller is a stand-up guy and I am not worried about that aspect. This is a hard call. I appreciate everyone's patience with my rambling and your expertise / examples / observations.