I can fill in some blanks on the 40XC. They were made for Highpower Rifle Competition. As mentioned above, they came with clip slots for loading for rapid fire. Earlier 40-XB were also used for highpower and came with clip slots. The 40-X rifles never really took hold for highpower rifle because they didn't feed or cycle as slick as the Winchester M70. To my knowledge, they 40-XC's weren't produced for the Army for Cross the Course use. Although I believe Gary Anderson shot a Remington for 300M International Competition. Albany Mountain...is it possible you have Anderson's rifle?

Winchester produced an M70 International Army Match that was used in CISM competition and those are collectible and somewhat valuable. Remington 40-XC, not so much. The XC's initially came with Wood (Birch I believe) stocks, but later came with McMillan Kevlar or Fiberglass stocks.
Re the 40-X coming in a long action version. I've never seen or heard of one and last I spoke to the custom shop, they had never produced one. I'd like to see a pic as well. When German Salazar wanted to put together a prone gun in 30-06 to match his 308, he had to use a M700 because the custom shop said "no go". I have a 40-X prone gun in 7 Rem Mag. It's a solid bottom and it's definitely a short action. No problem ejecting fired cases, but ejecting live rounds takes a bit more doing. It's been back to the custom shop for a new barrel and they screwed on a Hart.
Re the 40-X coming off the same line as the 700's. Maybe so, but at one time the 40-X came with a 1/2" accuracy guarantee for certain calibers. The 40-XBR was given special treatment and the receiver markings were etched instead of roll stamped because of the potential for distorting the receiver. You have to remember that Mike Walker was a big presence at Remington and he was a big benchrest guy that drove the 22 and 6BR, Remington Benchrest Bullets, BR Primers and the Remington BR Scopes.
Finally Warren Page gained access to the Remington Custom Shop test records encompassing hundreds of 40X rifles test groups. At that time, the 40X's in 222 Rem AVERAGED 0.363 inches, the 222 Rem Mag groups AVERAGED 0.387 inches and the 223's...0.400"...Hardly what I'd expect from a run of the mill Remington 700.