I think that you will find that a simple j-pipe turbo will be alot cheaper than a conversion. A turbo a15 will still go like the clappers on 8psi with not too much more than a decompression plate to the long motor.

In terms of conversions, there are a few factors. In NSW at least, I dont believe you can get a 1.8 litre turbo registered because of the weight of the car. So this rules out the ca18det, leaving you pretty much with the ca16 or toyota 4age.

Then there is the weight of the engines. They are both more than 20kg's heavier than an a series and as 1000's cant exactly change spring rates, etc, it could throw that out.

But heck, it would be a bloody exciting thing to drive!