Hi 257-

I think you’ve about summed it up, unless Seewin or someone else can add more (maybe a photo?).  

There was indeed a “three-line” roll marking die used on .270 WIN FWTs for a period of time around 1955.  I suspect that it was a variation produced in one run of dies that was not replicated subsequently.  Whether that was one single die or several in the same batch I do not know…  It is as Rule described, with the “Made in U.S.A.” moved underneath the words “TRADE MARK”.  I have a .270 WIN SG FWT with that marking and have seen one other FWT so marked.  Both were .270 WIN.  My rifle S/N is 398707 (1957 receiver) but the ‘SUPER’ marked barrel is earlier (’55).  Unfortunately, the gun is not here with me in SC so I cannot post a photo of the roll marking on that gun… 

To try and answer your questions, note that after 1952 the roll marking dies used on M70 barrels were one-piece (including the caliber designation), and the Featherweight barrels were marked as such, so FWT dies were not used on standard rifles.  I am only aware of these “three-line” dies on .270 WIN FWT barrels.  I cannot exclude other FWT chamberings (or standard barrels), but have never seen one that wasn’t a .270 WIN and a Featherweight.  Do you have such a beastie???

As for rarity and/or impact on value… They are certainly uncommon, but I doubt it would cause much excitement except among the geekiest of M70 collectors (like me)… 

Hope this helps,

Lou