Ross, this discussion took a turn and a fenton manifold with dual carburetors is the current subject with m.patterson56, not the 8RT-6520 you have pictured.

 

I dug my original manifold out this morning. Haven't seen it in years! Yes, it has the two bosses as in your photo but my current dual carb manifold does not have them - only the small boss shown in my photo where the brass fitting is. I don't think this boss will work. On the old manifold, it looks like the vacuum is taken from both venturi's. I doubt the small boss on the dual manifold does that.but I'll have to pull the carb off to see (which I will do tomorrow) I might just have to buy a couple of spacers, plug the front one and take my vacuum from the spacer plate on the rear carb. I guess it's the only way to know for sure if it will work. Thanks for your help, by the way! Mike