If you want the original number you will have to buy the original number as a personalised plate and will have to re register car and then put your personal plate on it
Usually the list of mods for the 1.8t are:
Down pipe
Diverter valve
Turbo intake pipe
Air filter
Remap
Running 20psi is pushing that little k03 pretty hard and with a standard down pipe and cat it's probably getting pretty hot.
Should be about 200-210hp with the above mods done
My brother had a manual 3.1 bighorn, went pretty good after a new exhaust, boost and fuel increase, had a set of 32" tyres on it and it went well off road. Quick look on trade me and theres a couple on there for around $3k
This guy looks like hes got a few spares
https://www.trademe.co.nz/motors/motorbikes/parts-for-sale/engine-components/listing-1860015347.htm?rsqid=c0b813e07e34426d82d51589cd462cd9