Not sure about the 1G-FE engine but nearly every other Toyota engine that uses a belt you just align the crank/camshafts put a new belt on and drive away - no engine damage.
The only one I can find is here:
http://www.parkingsensors.co.uk/taurus.htm
It hasa foil aerial - you really need one that will use the bumper bar. Rodders has one fitted to his GS.
They have some drawbacks - can be affected by rain and don't detect objects unless the vehicle is moving, but look much better than ultrasonic sensors.
Yes you can get the microwave / electro-magnetic type which either have a foil aerial that fits behind the bumper or uses the metal bumper bar as the aerial.
The procedure is quite involved. Lots of things to take off and because it's a twin cam engine the head bolts sit under the camshafts so they need to come out along with their followers and shims which all need to be kept clean and in order.
The biggest problem with be the exhaust as the bolts may be rusted on and what type of socket is required for the head bolts?
I think it would be worth stripping it down yourself, try and determine the damage before buying any parts. It may be cheaper to find another engine to swap if there is a problem with the head or block. The head gasket kit itself may be quite expensive.
Craig if you are going to have a go let me know, I may be able to get a day off work to give you a hand.
Best to speak with TDI or another tuning company. But I believe there have been people who have UniChip/HKS/Apex fuel computers installed and they have made a difference.
The ECU has various sensors and a pre-programmed map in the software. Using the values of the sensors it looks up the correct timing and fuel to use at any one time.
In closed loop mode it uses the information from the O2 sensors to adjust the fuel mixture to achieve the best air/fuel ratio. It does this many times a second so if you modify the MAF sensor signal, for example, it won't make much difference.
In certain conditions closed loop mode is not used because a different air/fuel ratio is required - e.g. when the engine is cold or when accelerating. Then the ECU just uses the input sensors and its pre-programmed map. If you alter an input sensor in this mode it will make a difference.
This is why you see better fuel consumption when you fit a Unichip/fuel computer because Toyota normally over fuel at high revs under acceleration.
Try Michelin Pilot Primacy. My boss had Michelin Pilot Sports on his Audi A3, he drives like a complete ****, and got 40,000 miles out of them. The Primacy are meant to be quiter than the sports and harder wearing.