Sorry for the delay getting back to you, I was out of state for the weekend visiting family.
Well, in terms of the mauser, I will have to pass on doing the barrel work for you, I need to keep my focus on the project rifles. But I'm happy to help you get the project done. In reality, I am not a mauser expert, and actually had a local mauser guy do the barrel mount and head space. It was worth the $70 just to have him do it, saved me time by not having to learn it on my own.
In terms of the Turks, they are 8mm mauser. What it is originally doesn't matter, you are just going to chuck everything but the action in the trash anyway. You need to be careful with the turk actions, they are large ring design, but small ring barrel threads. So, you will not be able to use any of the Mauser 98 surplus barrels. The Swedish Mausers are model 96 design which is the small ring, and is why I was able to buy a surplus swedish mauser barrel and use it on the turk. Now, you can get a barrel from any of the barrel makers out there (Douglas, Hart, shilen, MT Rifleman, etc etc) to fit a turkish mauser action, but you will pay a lot more than $75 which is what I paid for the surplus barrel. The other thing is that I have hear nothing but praise for the swedish mauser barrels, so in essence, I knew I was buying a premium grade barrel, at surplus price. And it held true, as the rifle shoots sub MOA.
The turkish actions are large and strong, but they are made with old school metalugy, so I'm not sure if I would be loading Lapua Mags in one, but any of the med range cartridges should be fine. I might be overly conservative on this....
Let me know if you have other questions.