165/35 Rear air shock & short cranks for 24" kids bike build

[Acnescar]

I'm building up a full sus 24" bike for my 10 year old that will actually work for his weight

I've got most stuff now but need a rear air shock that works - I can do an oil/seal change but it does need to work. 165 eye to eye 35 stroke. not worried if its battered just needs to be economical.

Also I've got a hollowtech chainset but the cranks are 170 - and brand new! would be happy to swap them for shorter cranks if anyone has some short hollowtech cranks - not sure how short they come though?

Thanks