Interesting stuff!
Savage was making the 99C in 7mm08 at that time, so doing a 284 would have been easy if they had the magazines I think. Most guns in that range have white line spacers, but not all of them. There's a number of weird configurations that show up from the mid-80's. Case colored or blued lever?
If it's factory, it could be somebody at Savage made it up for themselves, or it was a special order that they decided to make (maybe a small batch of them?). Or a gift..
Here's a 1987 99C that I picked up as an example of oddities, and probably looks a lot like yours except for the recoil pad and lever. In 1987 99C's shouldn't have finger groove forearms and should have a recoil pad, but it apparently got a leftover stock/buttplate, and got put together with a blued lever that didn't happen until they started having 99C's made in Spain.