How bout you just start off making exhaust manifolds for the A series engine, for the smaller A12's and larger bros A14/15's first? And utilizing the Garrett T25 for matching up the flange to the manifold?

This would be the simplest way first surley then worrying bout the carburetion sides of things. Which leads me to my next question, is this suck thru or draw thru setups? Will it be using the stock inlet manifold?

I think you better set your boundaries before embarking on any project. Knowing what you/customer wants would be beneficial before starting the fabrication side of things.

Dave