You should be able to use the straps from rads on Luminors no problem if you take the tubes out.
All the straps I've made for my 24mm watches are actually 26-27mm as I think it looks better than the skinny 24mm. You can use the bigger, nicer buckles with them and it also holds the watch better into place, not that much wobbling on those big submersibles like the 243.
If it's made out of 100% good leather then it should be flexible enough, you don't need to make an ugly tapered cut into it. What I do is hit it gently with a rubber mallet on the sides in the lug area so it will compress to 24mm without noticeable tapering. Sometimes I use clamps to slowly compress them without getting wrinkles.
All these I've made are 26-27 mm and I can take them off the 24mm lugs, flex them a while to stretch them back to 26mm and put them on Rads
http://forum.replica-watch.info/vb/showthread.php/building-strap-for-127179?t=127179
Of course with time some wear will show in the lug area if worn on 24mm.