A bloke called Ian Oglevie runs a datto 1200 in rallies up that way and is ballistic fast. Still A-series motor, too. Almost did the last QRC round that TCAC ran a few years back, but sadly cancelled due lack of numbers.
My 3K was out to about 1360cc's. We could have bunged it out to just over 1400, but that would have stuck me up a class. (Although it now has a 2TG)
You'll find the tarmac regs on the CAMS site. As far as the homologaion papers go, I think the scrut is being a bit over the top. All you need to prove is that the engine came with the car, and the factory manual can do that for you. It's also a recognised document, and perfectly legal to present for compliance.
There's a couple of Corolla's down this way competeing in rallys, but most of them (including both my cars) are 2TG powered. It does need to be said though, that I ran my 25 for about 15 years with a 3K, and was reasonably competitive in most thngs it did.
Cheers,
Rob