Didn't know you'd worked at Marlin Kutter; great information. In regards to Marlin employees, never knew any of these guys personally; but learned a little information during my Charles Jerred research. The last surviving employee from the Smith era I could identify was Joe Smith, and from a video interview of the man he began work there after being discharged from the Air Force at the end of WWII where he'd been member of a bomber crew flying missions over Europe. Said jobs were extremely difficult to find after the war and his job at the Smith gun works was the only job he could find. He worked there as a checker; and since he was unskilled when hired, was assigned to checker Field and Ideal grade stocks loaded on racks of 36 each; his quota was 3 racks each day so he was a very busy man if all those panels were cut by hand. While there he made fast friends with craftsmen in the engraving and high grade checkering departments and was slowly building his personal gun; a 12-bore ejector, single trigger gun with raised gold inlays and scroll on each lock plate featuring depictions of his dog "Smokey", and the name "Smokey" is engraved on the trigger guard tang where the serial number would normally be located. Marlin closed the gunworks before his gun was completed, so it has survived in much the same condition as the Jerred Deluxe.
I agree with your description of the installation of reassembling a Smith gun; it's a pain, but I purchased a device several years ago at the Southern that is a great aide. It's made from a pair of long-nosed (needle nose) pliers; one of the "needles" has a rounded tip approximately 1/8" x 3/8" long (I'm guessing) while a flat bar has been welded to the opposite tip and covered with leather. With the frame upside down in the vise and the trigger plate and safety aligned as you describe, the "pin" end of the pliers is slipped in the hole at the bottom of the opening lever and the padded side positioned against the side of the frame; a simple squeeze slips the opening lever post into alignment with the screw hole in the trigger plate and allows the trigger plate to snap into position in the bottom of the frame. Don't know why this device is not in wider use?
As to Marlin lever guns, honest walnut and blued steel combined with the ability to top mount a scope has always appealed to the deer hunter in me; I've taken many N. GA deer and have a fair number of Marlin lever rifles is a variety of calibers. My favorites are the late 50's/early 60's ADL models with the Bishop stocks; but the best shooting Marlin lever in my opinion is the short-lived 338MX model. I lost interest in new Marlin lever guns with the Remington acquisition; but in that regard let me add this information. It had, as you noted, been common knowledge among employees that the company maintained a vault containing experimental model Marlin guns as well as a fair number of Smith shotguns in various grades and gauges; some had apparently been returned for defects, while the others were just old inventory. Just before the Marlin sale to Remington those guns were sold, and thru connections, a friend got a list of the Smith guns on hand; there were just over 30. Those the company had judged damaged were scrapped, but my friend made an offer on the remaining 18-19 gun lot and purchased them all. Some of the guns scrapped were desirable models that could have been easily repaired, but he was not allowed to bid on those guns.