Yeah Rae's right.
The ABD is the same bore as G40 but a longer stroke, im not sure what you can bore a G40/normal engine to, but It would seem that you can go to that same bore with custom pistons from JE or wherever. You could also design in whatever CR and combustion chamber shape you would want there.
The ABD rods are weaker than G40 ones but they are still pretty strong rods, as long as you dont rev the thing too much then there is no reason why you should have to upgrade. It might be possible to use polo rods with custom pistons on the ABD stroker crank, but if possible this would require a bit more engineering.
carb plate I made
Personally I would (or rather I did) start with a normal 1.3 spi engine, get all your turbo on and everything, fit a decent clutch (my standard one wouldnt handle more than 0.8 bar) get it all working sweet how you want it.
That way you can learn about tuning your own engine without worrying about destroying it (which you will have to try hard to do) and when you have maxxed it out in terms of power (which will shock you anyway, I could see a standard 1.3 spi crack 200bhp if you wanted to do it) then start thinking about somthing different.
You never know, you might be like me and discover that anything more than about 170bhp makes your car total shite. Not being able to floor a car on the road is boring as hell, ok on the motorway.
Just make sure you know the principles of the operation and try to build up a good knowlege of how you set up turbo cars before you start.