I would definitely go for a nice thick custom made job for your install, you may as well get a custom intercooler whilst your there! space is tight so it would be very beneficial to choose the inlet/outlet positions

You will have lots of heat issues with that motor unless you get the cooling bang on, but I'm sure you know that anyway :D

Indeed going for a custom top intercooler with a seperate airflow from the rad this will exit on the top of the nose cone, two oilcoolers one behind each front wheel. was hoping that could get away with a stock small rad. So guess custom is the only real option. Is there any way to work out rad thickness/ capacity for engine size?

Not that im aware of but im sure there will be a way

Maybe a good starting point would be the surface area and thickness of the donor rad, but it will also depend on the ammount of airflow you can get to it i suppose

Good timing, just thinking of what rad to use, so I have bought one from this guy off ebay. Bargain!