dutra manifolds vs header

I have a set of Dutra’s on the slant in the D150, and yes it would seem that Dutra’s would flow better than a stock exhaust manifold, but also consider:
1) Dutra’s are really heavy, they are thick cast iron, will last for ever but weight about the same as a stock exhaust manifold.
2) For all the money that you will spend to get a set of Dutra’s, you really only have the first couple of inches of an exhaust system.
So if you can weld, it may be less expensive to buy a slant six header flange from eBay then make your own custom turbo exhaust. If you don’t know how to weld and you will be paying someone to fabricate it for you, I would have the fabricator price it both ways, 100% custom fabrication vs adding on to twin Dutra’s.
If I was going to turbo a slant six I think I would port-polish-clean up a stock slant exhaust manifold and make a simple J pipe to connect it to the turbo and use the money saved to spend on improved: ignition-timing-fuel controls.