Im swapping the standard dash loom in a GLi to the mont one...and was going to put in climate control....is it worth doing?...is it possible to use the existing heater air/con with a mont loom or will I have no choice but to use c/c?

yes it is worth doing, i have done 6 conversions , one days work, need prts , di it yourself save money

When you replace the GLi loom for a fairmont, you'll Loose the generic plugs for the Standard Heater controls.

Yes, you can retrofit the C/C into the car and use your existing heaterbox.
You'll need all the parts for a straight swap.
ie: Fairmont dash loom, BEM, Headlight switch, (remove a resistor in your dash) and all the CC parts.

As above its a full days' play, (not even) and worth it imho

Or obviously you could run a few wires and retain the GLi heater controls and have the fairmont loom.

Krytox is right TruBlu, krytox helped me do mine and it was the best thing amongs other things we did to my gli... Just do it!!!