That's a really nice M.1903.

My 1927 M.1910 in 9,5x57 M.Sch has the same arrangement of a removable horn pistol grip cap with the same sight wrapped in newspaper. It's 10 thou different to the fitted sight and there's at least 1.5" change in group height by changing sights. To remove the fitted sight on my rifle, I have to drift it from left to right.

Mine doesn't have the multi-leaf standing sights like yours but an early factory catalogue shows they were an optional extra, perhaps fitted in this case for Heyer. In other respects, including the take-down pin and lever, it's the same and it was known by the Steyr factory as their "English" model. As to my barrel length, it's either the same or similar, I'd have to check. The M.1910 has a steel buttplate rather than a pad and this has a couple of spare rounds and a cleaning rod (take-down), under a trap. It also has a Baillie-Grohman peep sight that folds down when the bolt is cocked and then back up again.

I also have a 6,5 M.Sch carbine. I find that new or old 159-grain RWS bullets are undersize. Perhaps to fit some other German 6,5mm caliber also? I use an expander ball that I've turned down a few thou and this grips these undersize bullets, but accuracy is not flash and velocity is lacking. Hornady 160 grain .264" bullets are much more accurate and velocity better. If you slug the bore, you may be able to use Carcano diameter bullets as Handloader magazine recently advised. However, the Carcano bullets have to be loaded to a much shorter length or otherwise they jam in the rifling. This is because the forward part of the bullet is much less tapered than the .264" ones from the same company. Unless you have an OAL guage, and are a very experienced handloader, I'd perhaps avoid them. However, they do give good accuracy and velocity by obturating those rifles fitted with oversize bores. It seems that before 1945 6,5x54 M.Sch barrel lands and grooves were somewhat larger than those made after 1950, but assume nothing until your bore has been slugged.

I was in the Holland and Holland gunroom 25 or more years ago and this new Scottish law was about to come into effect. I was looking at a couple of 6,5x54 Mannlicher's but they expected others would soon become available. They made the point, a very fair one I think, that the 6,5 Mannlicher had probably shot more red deer in Scottland than any other except perhaps the venerable .303 British. It had also accounted for probably every game animal on Earth. So it is a very silly law.