I believe the rifle you have is a Model 39.
Just my guess from looking at the pics and noting small points about the rifle.
**But there are a couple things that still point to a Model 97. Disassembly would tell you the difference.

The 'Marlin Firearms Corporation' bbl address is common to just about all the Model 39 rifles.
A very few of the earliest may have the Marlin-Rockwell bbl address on them, but they'd be rare.

I think I see the 'bullseye' trademark in the toe-line of the stock. That was something that came about in the early 20's when Marlin Firearms Corporation took control of the company (1922/23?) and continued onward from there.
A Model 97 would not have that feature. (A 39A would of course)

Look at the tip of the magazine tube,,the 'cap' on the end.
Is the release on the end to pull the mag tube out a round 'button' imbedded into the right side of the cap? That would be a Model 39 style magazine release.
The Model 97 used a small rectangular lever in the same position that was pinned to pivot and release the mag tube when pushed inward.
You might find a few very early production Model 39 rifles using the Model 97 mag release..nothing was thrown away,,but it again would be rare to see.

With the Mod 39 button style release, the mag tube cap is about 1/2" shy of being even with the end of the bbl.
With the Mod 97 style release, the end cap is just about even with the muzzle of the bbl.
From the pic above, the magazine looks to be of the 97 type. But i can't see the release style (39 or 97) as that is on the right side of the end cap.

The standard butt stock for the Model 39 was the uncheckered, pistol grip stock as you have. The reverse 'S' curve on the bottom of the pistol grip was a standard stylized feature of the shaping.
The oct bbl was standard on the Mod 39 and IIRC was the only bbl made available,,no round bbl in standard production. (Never say never did they ever make any w/rd bbl though!)

Open the action and look at that ejector on the inside left reciever wall. The assembly is attached into the frame from the outside by those two screws I mentioned in the other post.
To avoid that problem of the ejector arm snagging the cleaning rod and so as not having to provide and use that small spring clip I mentioned to hold the arm down,,,Marlin redesigned the ejector slightly in the Model 39.
**A Model 97 would not originally have had the re-designed ejector as described below. The rifle would been to early for the redesigned ejector hold-down feature.

To see this redesign, simply look at the ejector assembly through the open ejection port.
With the bolt open, the ejector arm will be propped outwards a bit in it's position so as to eject the cartridge.
The redesign is a small screw in the assembly just ahead of the front tip of the arm. It has a cut/open space in it's flat head that allows the arm to work.
But if you depress the arm and then turn the screw a partial turn,,it will hold the ejector arm down and out of the way, safe from snagging cleaning rods and jags.

You do have to release it again afterwards or you get no ejection action when firing the rifle, but it causes no damage other than the 'oops' feeling of the shooter.

The Standard Vel ammo only still applies.
Only those Model 39 rifles with an 'HS' ser# prefix have the upgraded bolt assembly.
AFAIK, all the other Model 39 ser#'s were either w/o a Ser# prefix (like yours) or had an 'S' prefix.
The 'S' prefix is still a Standard Vel ammo only rifle.

If you take the rear tang sight off of the rifle, It should be stamped 'Marlin / Mod. 39' underneath. or 'Marlin/ Mod 1897 (97)'. depending on which it is
Some have an additional small star punched to the rear of that. That was their final QC/quality assurance type mark.

The 97 and 39 use a flat mainspring,,,the 39A went to a coil spring.
You'll have to pull the butt stock off to verify that one I guess.

So that's what I see.
The rifle could simply be a 97 parts gun assembled after they were dropped from production and the then new owners, the Marlin Firearms Corp had taken over. That was explained on the other thread.

If it's a Model 39,,or even ends up being a 97, with those sights and the decent condition, exc bore & mechanics, ect. it's probably a rifle that'd sell for just under $1k around here.

As I said,,that rear tang peep sight and the Lyman folding front sight are together worth about $400 depending on condition.
The rear tang sight also fits the Hopkins & Allen single shot rifles and IIRC the Meriden Mod 15 pump .22.

Not in the collector type condition but certainly a desirable rifle.

A shooter may pass on it because of the SV only ammo thing, but there are plenty of vintage rifle people that'd be drawn to the rifle for it's originality.

I've never had a Model 39.
I did sell a late production Model 97 standard round bbl rifle, straight stock, exc bore, standard open sights. Metal and wood appearance about the same as this one. Sold for $600 but that was nearly 10yrs ago.

The rest of the bunch I've managed to hold on to.
Hope this helps.