I've thought about doing this before (and still want to, so I'm paying attention). It would depend what kinda of fabrication talent you have and wether you have access to the right stuff. It would be better to use a header type manifold for the exhaust, but you have to ask yourself if the time and money wouldn't be better spent elsewhere. If you are set up to make a manifold go for it. To have built though........I have a feeling it would get prohibitively pricey pretty quick.

What kind of induction are you using with your turbo? Draw through carb, blow-through carb, throttle body injection, port injection? And for boost controls? or are you even using boost controls? Intercooling/aftercooling? Size of turbo? I've done a bit of research and I kinda wanna know what you're planning.

Here's a good site for ideas:
http://www.megasquirt.info/

go to the page on turbocharging your megasquirt, the ideas apply to any engine.

more to come when I have a few more minutes.....