Can anyone confirm the mapping between these - my interest is peaked now. even if the wiring harness is similar enough that I can swap out the ECU with the bottom end - that would be SWEET!

See now this is what I was wondering.  IS the plug (ecu) for the 2.0 wiring harness the same as the 1.8 harness.  Are all the trannys the same for the 2.0 and 1.8 auto's  Am I making sense?  SO esential swampping a 2.0 motor into a 1.8 sidekick only changing the motor and ecu for proper functioning. Is this off the wall???

Yes, the trans are interchangeable.

The only easy way to make sure it is running 100% Factory is to swap the ECM. Another option is to use a piggy back or interceptor but you need dyno time to dial them in but it does mean you can optimise what you have but it will cost more than just swapping the ECM.

The 1.8 and 2.0 are a pretty close match and I wouldn't be too worried about using a 1.8 ECM with 2.0 engine but the 2.3 is a bit of a jump and I'd be wanting the ECM to match.

FYI Suzuki actually fiited the 2.0 in other markets but North America got the 1.8 at that time due to emissions issues. I have a swb with the 2.0 from the Factory.

Our lwb had a 2.0 V6 (had one of them too and some markets even had it in the swb) which later became the  2.5 and 2.7 in the GV & XL-7. Others have swapped the 2.5 into the 2.0 V6 and kept the 2.0 ECM and that worked fine.

Out of curiosity I googled "Suzuki J23A" the other day and found a site showing pix of a 2.0 l swap from a 1.8.  (I didn't save the link)  Some mention was made of using the 2.3l engine.  Apparently the 2.3 ECM is not compatible with all the electronics of the 1.8 and 2.0.  It might be possible to make the 2.3 work with the older ECM by swapping other parts, but I get the impression that the performance would suffer.
Does anyone know what harness mods would be required to put a 2.0 ECM, or maybe a 2.3 ECM, in a Sport when swapping engines?  I guess that a guy could study the schematics of each vehicle before starting.  If I could eliminate the wife's honeydo list--fat chance-- I would like to take on the project.

is a junkyard engine a good place to start out?  I am rusty but would love the chance to get dirty building one again

 The main person you would want to ask that would know about the wiring/ECM differences/swap for the Sport would be Brent at Trailtough. Ask, and he shall know.