Raj, I own a ListerBell which has the Toyota 2GR-Fe engine and has a new registration through the IVA process, My registration number would be on a 16 plate but I have a private reg V66STR, I wanted V6STR but Craig has that :-). My car has 325Bhp which is very easily achievable using stOck ECU, I can confirm that the car is very Driveable with the quad VVTi and drives like a normal car until you boot it when it turns into a bit of a monster. The sound in the cockpit is incredible and the high revving V6 suits the car probably being more like the Ferrari engine than the Alfa which whilst an awesome engine in its time
is a bit of a thumper. It's a personal opinion but you are going to spend a fortune piddling about trying to get 325-400 HP out of the Alfa engine, even using a new Toyota engine you will probably do it cheaper and you will end up with something super reliable with arm wrenching torque. I can confirm that for new registration for IVA you are allowed 1 rebuilt to as new component. If you go to IVA with receipts saying both engine and gearbox have been rebuilt then you should not get a new registration. I was very careful that my documentation said that my engine was new and the gearbox rebuilt, they are 2 separate components. End of the day it's your decision, and that's the beauty of it. My ten Penneth aim for 250-300 Hp, it's not all about power, you need to spend money on upgrades to the suspension and brakes and having it set up properly otherwise you won't be able to enjoy the power the engine does have. I have a build thread on here if you are interested.
Rob