Just a question.Will a 9 speed chain work with an 8 speed index system.It looks the same width to the naked eye
9 speed is narrower, years ago I tried this and it won't seat properly in the cassette.
Don't know if this is much use to you but I once swapped from 9 to 10 but swapped back.
I then used the 10spd chain on the 9 spd block - no probs.
So, technically, try it..what have you to lose ?
It should be fine. I'm running a 10 speed cassette and chain with old '7 speed' chainrings. The only time I think you are going to have problems is if you try to run any 8-9-10-11 speed chain on a single speed set-up designed for 1/8 inch chains.
I use the same chain for 6, 7, 8 and 9 with no issues.
I believe the 10 is narrower and the 11 entirely different.