It is authentic, but it is an interwar rework, which is no great surprise. Hate to place a value on it as it is a rework, but it is "matching" and it has a desirable unit marking also, so two things working against the other... to the right collector it would be worth stretching for it, for most, maybe not too much.
It looks like it is a thorough rework also, probably bolt is original to the action (but blued), the rest is scrubbed and re-numbered to match, but it is authentic to period imo. Most of the work is very typical of depot work in the interwar period, where they typically scrubbed parts and re-numbered to match, also scrubbing stocks and the old markings faint perhaps but clearly removed and the new numbers and acceptance sharp and often over the old markings. You have a HZa (depot) stamp at the wrist, hard to make out, but they probably did the work. If you can do a good picture of the HZa mark, you might know who reworked it. Not a big value point, but might mean something to someone and does lend credibility to the work.
There are a few of these known (DR's), this might be in the best shape of those known, so that is a plus too. Interwar rifles, reworked or not (most were to one degree or another) are hard to find period "matching", yours has it all, looks all period done and in one piece, with a desirable unit marking.
If you feel adventurous, you might look under the handguard or stock, it might have been re-barreled, which typically doesn't tell us a great deal as I do not think many barrels were made in the interwar period (for the 98a) but it might have a clue, a new FP or something that tells you more. Some interwar 98a have unique barrels, Police marked ones especially. Think about this carefully though, removing handguards and stocks on the 98a, especially for the first time is problematic, it isn't difficult to damage the handguard..
