I think this is the thread about the Hart barrels that I referred too. https://forum.accurateshooter.com/threads/hart-barrels-on-factory-remingtons.3756178/ One thing you also need to keep in mind is,if Remington did put any special barrels on a limited amount of rifles back in the 1960's,the people who would know for sure are likely to be dead or long gone from the company by now.Remington did have a history of making dealer exclusives and special run rifles.I have a special run Remington Sendero I bought used in 2008.I called Remington to find out what I had bought.They told me it was made in 1996,it has a laminated wood stock and a blued heavy Sendero contour barrel,but does not have Sendero stamped on it.The barrel stamp shows it was done in Madison,North Carolina.It's chambered in the 7STW,I think the same year Remington introduced the 7STW chambering in their rifles.He told me it was a special run or a dealer exclusive,non catalog version of the Sendero rifle.They were also chambered in the 7mag and 300 Win Mag.The transition from hard copy records to computer records probably started in the late 1980's.If it's not in the computer records,a lot of the prior hard copy records were probably were never entered.
[Linked Image from i.postimg.cc]

~Molɔ̀ːn Labé Skýla~
As Bob Hagel would say"You should not use a rifle that will kill an animal when everything goes right; you should use one that will do the job when everything goes wrong."Good words of wisdom...............