Hello mate. When I did mine I used the C20LET engine which is basically the Red Top Turbo. Quite hard to match looms but almost everything else was a straight fit. I used the same SRi brakes and suspension I already had on it. You just need to spend alot of time with a circuit tester matching up the wires.
The btter engine
IMHO would be the 3.0 V6 which is 210bhp or the 3.2 V6 which is 217bhp from an Omega. I have beaten so many turbo's now with my Calibra 3.0, including a tuned scooby. Better fuel consumption and part are still readily available where as the red top parts are getting very hard to find. Plus you will only pay about £350 for a 3.0 where as you will pay anything upward of £1000 for a turbo lump with less power.