Thanks for the replies gents
After driving the triton today again I feel that the performance of the engine is fine if you keep the inlet manifold clean (provent 200 coming soon) so I have pretty much ruled out a chip/engine upgrade.
I'm still not sure which end the diff lock would go yet, although I know the front locker will get me further than the rear one I figure that if it can't get up with rear locker, front TC suspension lift and bigger than standard muddy's then that's what the winch is for. Having never driven with a front locker I'm a bit unsure of how much the front diff/CV's will take before busting something (not doing anything crazy).
As for the reduction gears, Marks 4WD still advertise them for sale on their website (as well as the Pajero ones as well) and there is nothing on the page about being out of stock or anything. I will probably ring them soon and find out what they do/don't have.
If they were unavailable anymore the only other option would be do swap the diffs for 4.11's to get slightly lower gearing (I know 4.6's are the go but they are hard to find).
Not being able to lower the low range gearing even a little would be a deal breaker for me as far as keeping the triton would be concerned.