I have a
6.5x53R, in a good condition Steyr military rifle, people tell me is to good to customise.
6.5x54 Steyr or M-S, a Greek mil rifle customised, Possibly suitable for more customisation.
I've shot either.
A M38 or M96 in 6.5x55, which I've used a reasonable bit.

But I bought a 6,5x65 barrel for my Mauser M03 switch barrel. When I couldn't get a x68 barrel. Akas that barrel is only 600 mm and too short forvrechambering to x68.

My 8x68S barrel is another M03 barrel as is a .404 and a .222

I have two M03 rifles and would love a 6,5x68 barrel for my M03s.

As long as it shoots 90 gr to 140 gr bullets at ultra velocity, 650 mm barrel is mandatory.

Your rifle is quite nice. Good luck with it.