When a gun uses an en bloc clip or a removable magazine, the feed lips and initial guiding of the round, as well as retention of the round, are built into the clip or magazine. There is usually also a feed ramp designed to handle the appropriate bullet and guide the cartridge once it is released from the clip or magazine.
But rifles made with a built-in magazine, like the Mauser 98, have the primary guide and cartridge retention built into the side rails of the receiver. That is why changing a Mauser or a Springfield M1903 to another cartridge can require work on the feed rails as well as on the ramp to get proper feeding.
There is also a third way, used by some sporting rifle makers. A magazine box is inserted into the space between the receiver and the bottom of the magazine well; it has the feed lips and guide built in; this allows the maker to change around among similar calibers by changing only the magazine box rather than the feed rails, an easier proposition.
For your purposes, it seems to me the problem is not proper feeding but retention of the round in the magazine. To do that requires not only rails of some kind but also a properly shaped follower, plus magazine walls to guide the rounds. Just fixing a clip in place might work, but it would be difficult to load the rifle and, as you note, the clip would soon wear out.
I suggest studying magazines like the Mauser and the Remington 700 and seeing if a magazine box of some kind can be rigged.
Perhaps some of the other folks have done this job (I have not) and can tell you exactly how to do it. Lots of luck.