Op Rod Cuts

Over the past 40 years have amassed a collection of guns and spare wood.  Finally want to best assemble a few guns.  Have a 6125XXX Underwood.  Using a type III, P-U stock, and 2-rivet P-U hand guard have a 1/2" mismatch at front of operating rod cut.  Comparing rod cut to several other 2 & 4 rivet hand guards find all same.  Have type III, IV and V stocks with OI, W, TN, and SA manufacturer's markings. All closely match any hand guard.  Why would the P-U stock be different?

Thanks again for sharing your bottomless knowledge base.  Yes, it has thinner wood and with 3-3/16" barrel channel as illustrated.  Guess it could be a modified type II?  Otherwise the stock is unmolested having sharp corners, no cracks, rebuild marks, and a faint, crossed cannon cartouche.

I have two stocks that have about a 1/2 inch difference between the stock and handguard at the front of the op slide cut. One is a J replacement stock the other is a M-U which was possibly a type II converted to type III. They are what they are, If your P-U stock was mine I'd leave it as it is.

I had already stripped the old finish with Formby's Refinisher.  Works fantastic!  Extended cut with and an end mill for a good match.  Will start applying four coats of raw linseed oil today.  Gun is no museum piece.  Import marked I paid $100 for at an estate sale.  Just want to add it to the collection as a more or less period correct example.