There are a few things you need to take into consideration when looking to use a fly reel as a centerpin,
1. How much space between the spool and the frame, now having used mono running lines in everything from 20lb to 60lb from multiple manufactures there is something called "pull through" which means the line passes through between the spaces on the spool and frame and gets caught in the spindle/ spine of the frame which will cause you to break off from that point, to which you will loose your running line, shooting head or just basically everything beyond that point. A Milner for example is manufactured with such tight tolerances that it's very hard to get any line between the spool and frame, sometimes we all get a little birds nest when casting, and the bottom and top of the frame will hold those loops and those loops will in terms pass through and you will have problems.
2. Packing on the backing cause most fly lines are such a large diameter that it takes up the space between the backing, backing is cheap but you will be winding on more to get that space to give your reel the space needed to take up line properly.
3. Finding a fly reel that will work, but from the sounds and looks of it you have a candidate, just need to remove the little plastic nubs for the clicker and it should work fine.
I hope some of this helps out.