1.6 geearbox

what the difference between a 1.6 and a 1.8 gear box and if any will a 1.6 be ok on a 1.8 engine

both engines came with carb or injection, and the carb models could be had in auto - so you'd need to clarify if you mean GTI (injection, manual).

If so, then the final drive ratio is different - 3.89 for 1.6 and 3.67 for 1.8 models. Later Mk2 GTI 16V Golfs had a slightly raised 2nd gear, this was so they reached 60mph in 2nd (not requiring a gearchange to 3rd) so their 0-60mph times looked more impressive in magazines and brochures.