G'Day
Just a few ideas for you to think off.
The ADM Delivered Toyota Corolla Sportivo is a southafrican built and assembled Car, from the Durban Toyota Plant.
All the Sportieve Corollas are Southafrican. The Normal 1ZZ corollas are (not exact figures, but approx) - well... lets say, if at work (I work at Toyota) 50 corollas come in, maybe 4 or 5 will be sportieveos, 15 would be southafrican 1zz built, and the remanding would be Japanese.
Basically, they are a pretty poorly built and assembled vehicle. (the south african ones) There are a few differences between the Jap models and SA models. Eg. Different panels, Battery's, Hydraulic assemblies, interior differences down to a water washer bottle thats different. I guess they figured it was cheaper to make there own in SA rather than get them from Jap. *meh*
Anyway, back to where this is leading - Personally, if i had the $$ , and you obviously have some $$ to play with - and wanted to have the 2ZZ corolla - I would get one thats got as Little Kms as possible, and is still in warranty. Because, your going to want to have warranty with this car. Seriously.
To make it go harder, as such, First thing i would do, is do some research onto what different gearboxes you can get. Simply because the ratios on the sportievo's box's are horrible. You get up into power band, change gear, off cam again. and they are such loooong ratios. I don't think its the final drive which is the real problem. But thats just my experience from driving them.
2ndly, this clashes with my first recommendation of warranty. Id be pulling the Cyl head off, and sending it to a machine shop. Get the thing ported and flow'd properly. Get the head shaved. Get the valve angles attended to. Etc. While you are at it, see if you can get a different camshaft setup. One that has the Lift kicking in earlier, and a more aggressive profile for the 2nd part of the cam (the high RPM setup).
3rly, Now, as the computer may be having a fit from what you have done to it, id be pissing that standard computer of anyway. Aftermarket for the win.
Remember, if its been done to a new celica, your corolla can have the same, provided physical size constraints are not a.. problem ;)