You will have some clearance issues between the rear Dutra and the starter. I have the full Dutra duals, and a mini starter, and still had to do some grinding on the exhaust flange to get clearance. I wrapped the starter for heat, but eventually the wrap fell off, and I never replaced. It has not been a problem, but the wiring is very close to the rear manifold as well. There really is not anything wrong with using the front Dutra, and rear modified stock unit. You have carb heat with that as well, which gives better cold start drivability.
I had the rear stock unit for several years before I went to the turbo. It was the turbo that prompted me to get the rear Dutra. When I started planning the turbo project was when I purchased the rear unit. It was a year or so before I actually used it, and the entire project took almost a year to fabricate and get running. If Lou Madsen hadn't made a charity run up from North Carolina(he's now in VA) it might still be just sitting there.
My point is, once it is done one way, it is a big deal to change it. And, it probably does not make much difference. Don't let your machinist scare you. He most likely does not know the slant world, and its slanted engenuity.
Sam