I just rebuilt my 22, which had 270 on it.
I did it because the rest of the car was pretty good and I didn't want to just run another old engine with 150 plus kms and unknown history. Brand new's better
Not enough time to do anything fancy like finding a EJ25 block, or swapping in a DOHC engine (and additional parts). And, same as you, I had a fairly new timing setup and a new water pump.
I'd recommend it. Took about a week of avos but was a pretty easy affair, once I found some workspace and an engine crane. Only tricky thing was getting the gudgeon pins in an out, which, once I found reeely long screw driver was fine.
Cost was OK aswell. Most expensive thing was the head reco and Head gaskets.
Full Head reco $400
Crank polish and block bottle brush hone $0 Cause the dude doing the head was cool (Plug: Engine Rebuilders Canberra)
Rings, rod and crank bearings ~$200
8 new exhaust valves @$12 a pop
Genuine head gaskets $160
Water pump gasket $2
Tube of black Threebond $0 off a mate that works at Holden
Rear main ~$45
Cam seals ~$7 each
Crank seal ~$12
Service manual $0
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Thats pretty much all I used. The engine was a bit worn but its all in the consumables, bearings, rings and valves. These engines are pretty bullet proof.
Didn't prime the cam lifter assembly at all, or check for stuck lifters. I'd do that if I did it again. Took about an hour of running for the last lifter to pop. Sounded like an old magna tapping about untill then. Thought I'd stuffed something up, was so disheartened. Then elation! At least the rocker assembly would have been easy to take off in car.
Now the car goes like a champ! 1700km in it, no power increase I've noticed, might run a bit better down low but big winners are it doesn't leak like a siv anymore or comsume oil! Uses slightly less fuel and I know it'll do another 270,000 no worries.