The M03 magazine for the .404 will work with the 8x68

The ST bolt-head will work for both the .30-06 and the 6.5x65

65 cm barrel for the 6.5x65 would be special order. Not necessary if you reload, stick to the 60 cm.

M03s are barrel-heavy to begin with, and the 6.5x65 with a 60 cm barrel is quite a practical setup, good handling and not too long for a blind where longer barrels are a nuisance. I shoot Berger Bullets with a Norma MRP-2 charge out of my 6.5x65 M03 with a 60 cm barrel, get hole in hole accuracy and speeds exceeding a 6.5x68 at safe pressure levels. You only need the 65 cm barrel if you use factory ammo (...there is only one factory load,by the way).

By the way: The 6.5x65 is EXTREMELY prone to generate a doughnut at the inside of the shoulder/neck junction. So much so, that one German reloading manual advises against using anything but fresh brass. Before you start thinking about reaming the inside of your neck to remove the doughnut (which is necessary every time and screws with your accuracy) I'll give you a tip how to avoid that issue altogether. Take a neck-turner, adjust it to not take off anything from the neck itself, but grind into the shoulder by about 7/1000 of an inch. Your brass will look a bit funny, but it will not have an impact on accuracy or otherwise (just dont cut into the shoulder by too much). When you fire a round, the brass that normally forms the doughnut flows into the area of the shoulder which you had cut into, and your case will look normal again (and not suffer from the doughnut effect). You only need to do this once, - with this method, a doughnut will never form.