Welcome to the site Gib009!
How did you find your way here? (just out of interest)
I think a few people will be away for easter so you may not get a lot of response for a few days. I'm just about to head off too, so i'll have to get on when i get back and rave crap
Good choice with the Sierra, they're heaps of fun. Try find one with no rust or very little if you can, you can always replace motors and diffs, in your case with bigger motors and lockers
Crawler gears will cost you around $1300 new or as cheap as $700 second hand.
Spring over might give you about 4 inches lift, so you might not need extended shackles to fit 33s. If you're going to go bigger tyres, you might want to get a long wheel base as 35s on a swb will be a flipper

too short for the height, so hill climbs will be scary!
Mart on here has 35s and a 1.3, but with mods to it, and Series 4 crawler gears. He has extended his wheel base out to 90 or 91 inches i think. Mine is about 90 inches, and feels very stable on climbs. Ofcourse once you go bigger tyres you might want to upgrade your diffs, hilux, MQ etc. Some people run 33s on stock diffs, but if you are rockcrawling they wont work out too well. Probably ok for forest tracks and mud.
Lots of people do similiar mods and end up with different results.
oh look i've been raving crap already, i better go pack the camping gear!