Transmission help please guys

[MrHydeTattoo]

Hi all I have a 94 cr500 but am I need of a transmission as mine is missing!!!!!
Locally are loads of 85-88 complete gearboxes but I don't seem to be able to find info on compatibility between years....

I have found they changed ratio in later years but could I install a complete transmission from an earlier model (close ratio I know )I'd be riding mx so no dunes etc as I'm in uk

Thanks in advance