I own two of them. Both are standard models. One has a SN in the 3XXX range and has a 26-inch barrel. The other is in the 7XXX range and has a 24.4" inch barrel. In addition, I found one several years ago for a hunting companion who admired the performance of my rifle. His is the Deluxe version with a SN in the 5xxx range, I believe and also has the shorter barrel.
Apparently only a handful of the earliest production guns came with the longer barrel. I purchased the 26-incher I have just a few years ago and have not worked with it a great deal.
My 24-incher I purchased new in 1965 and have owned it ever since. With it I have killed everything from jackrabbits to elk, having taken coyotes, bobcats, feral hogs, whitetails, mule deer, pronghorn, and no telling what else in between. I use a 140 grain Nosler Partition as my only load. This bullet is propelled at 3150 fps with a capacity charge of WW-872, a surplus powder originally made for the 20mm gun. This gun has had exactly 21 rounds of factory loads through it -- a box of 20 Remingtons which came as a store courtesy with its purchase -- and 1 round of Winchester I put through it to chronograph (at a blazing 2800 fps). Accuracy of this gun has always been excellent, and even with untold thousands of rounds down the barrel remains so today. The stories of "barrel burning" in this caliber are greatly exaggerated. The gun with the 26-inch barrel will top 3200 fps with the 140 Nosler.
So far as I know, Sako dropped this chambering at least at the " Garcia" changeover in 1978, and may have done so prior to that. Come to think of it, I have never seen a .264 with a five-digit SN, although they certainly may be out there. Thus, all L61R's in this caliber are the three-lug bolt variety.
Yes, it would be fair to say that the caliber is "obsolete", as least insofar as factory ammunition is concerned. Unfortunately, factory ammunition never reach optimum performance in this caliber, so the lack thereof is little loss as far as I'm concerned. Actually, Ruger is chambering the caliber right now, and Remington has done so fairly recently.