I had a 7mm mag model 77 maybe 25 years or so ago, and loved it. But after losing my deer lease and all those bean fields, I traded it off for something else.
Then maybe 5 years or so ago I got really missing that Ruger and was in the market for a .270, which is how I ended up with the same ride you describe, but in .270.
I too was thrown a loop by the ebony tip, and started digging around. I think I have learned that Ruger made a lighter weight Mountain Rifle, that had and ebony tip. Mine is a shorter and lighter version of the old 7 mag, same tang safety, red butt, with the addition of factory sights and that ebony tip.
It's a great little rifle, and so handy. I'm thinking it's a 20" barrel, but can't say for sure without digging it out of the back of the safe. I think you have a unique and handy little rifle, and at a very good price.
If anyone knows any more about these ebony tip rifles, or can correct any errors, please jump in and tell us more. I never could find out how many were made, but I think mine came up as an '87 as well (I've got that written down somewhere).