The only thing I could offer is the upper webbing from a RCM8 (Ted Simmons) which has 4 lace holes at the bottom, instead of the 2 that's on the RL 10. I beleive it could still work. And a cloth patch in great shape.
I got a RL 10 Johnny Bench recently in near mint shape. But yours, sad to say, is frightening!!!

May the restoration gods be with you.