I am not on the FB group. I prefer forums, haha.
I can only recommend a twin stromberg setup based on what I'm using, which are dual NON-EMISSION ZS carbs. They're pre-69, which means they're adjustable jet models (from the bottom), with fixed solid needles. The ones I'm using are from a B30-based Penta boat engine, and I'm running TR4 '2A' needles, which seem to be working well for the B21A. I have no idea how it would work with dual emissions carbs (anything with a fixed jet height and adjustable needle), but I'm fairly sure it would work too, with tweaking.
I get great fuel economy (I mean it's certainly no worse than the B6304S that was in there before), and while it's not a road-burner, I've been driving it more now than I ever did with the 6 in it.