There are a few Mauser '98's marked R.Famage 1952 floating around Oz atm.

These are/were 30-06 rifles with a small notch in the top of the front receiver and the correct magazine length for a .30-06 with spitzer. I believe they may also have the full 'C' ring if that is important to you.

The initial outlay may be less than a ZKK. Safely re-worked, it then gets down to how much the gun smithing is going to cost.

I have seen Tony Small http://nickalguns.net/ extend a magazine ( it is quite simple to do ) and he may have pictures of it still. He can also make up the correct magazine spring length.