what turbo headers for a 318?

I like your idea of the SBC headers. Is the port spacing the same as SBM? It would definitely give you more options. The Dakota headers will not fit the passenger side when reversed. One of the tubes will hit the fender well. Drivers side should clear with manual steering.

Best of luck with your project.

Yes, I have found several people that have swapped flanges from sbc to sbm on other builds. usually hot rod guys that bought swap meet headers. so they must be close enough. I think this is the simplest route.
this is going to be a fun project! never turbo'd anything before as blow through carbs were always a mystery to me. but with the fitech or sniper..."how hard can it be" lol. I figure it makes enough sense to try. since they come on softer...the 904, 8.25, and oe converter aren't an instant concern like if I was just building a 450 hp engine. 8 psi shouldn't kill something with low factory compression....famous last words anyways :) lol