Yes, John Unertl copied the Unertl O & E off the WWI WRA Springfield Marine bases.
The blocks are nearly identical except for slight differences in the machining at the ends of the block.
They are nothing like the blocks on the Senich Rifle.
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Thanks for posting the auction site listing.
The rifle is definitely not a sniper rifle, nor did I ever claim it to be, nor did Senich. It's a rebuild.
If the rifle was an old match rifle, the elongated front base could have been used to switch back and forth from 7.2" spacing to 6" spacing, depending on the range of the match. Seems logical.
Just to add a little humor to the show, I laser etched a whole bunch of M14 parts with NM just for the halibut. Connector rods, selector switch, trigger group, sling swivels, sling keepers and a few bolts. I also posted along with these, don't believe anything you hear or read and only half what you think you see. Saw photos of my fakes used a proof by a few of the wannabes that showed how clueless they actually were.
With out formal research as cplnorton has done it is awfully easy to interpret other's writings as fact when they are often times based on the writers personal thoughts and not necessarily fact.
I took a silver paint pen, and had my wife (better handwriting) put PIETHON on the barrel of a new in box RG 22 short I picked up in an estate, and to a Jennings 25 that was chromed and with a gold paint pen had her write Gold Cup on the slide,
some folks at the gunshow got a kick out of it, some were confused