Exhaust question?
 

Would a mk1 saloon back box be ok for the mk2 hatch? I know it would be 6" to short for the mk2 saloon but as the hatch is shorter would this be ok?

It might well be ok, difficult to say 100% without comparing measurements.

Anyone ever tried it? Or got a mk1 saloon backbox lying around the could measure up for me?

A mk2 hatch is 4386mm long

A mk1 saloon is 4530mm long

Difference of 144mm

Anyone good with maths?

Do you know what a mk2 saloon is?

4540mm

10mm longer yet the skirt overhangs 6" (150mm) further, hence mk1 saloon exhausts completely disappearing under the bumpers of mk2 saloons.

So if a mk1 saloon backbox is @ 150mm a shorter than a mk2 saloon, should be good for a mk2 hatch, if 144mm shorter.

Riiiiiiiiigghhttt

It is very easy to either extend or shorten the tailpipe, a local exhaust fitter would usually do this for around 15quid.