Sorry for the slow response! Not only have I been busier than a one-handed paperhanger, but I also had a helluva time finding this thread so I could respond, as I kept searching for "air fuel", etc. instead of "AFR".
Anyway, I'm running this in my '68 F250: https://www.summitracing.com/parts/atm-3379
No special reason why I chose this one over the others, other than looks (I have a matching vacuum gauge mounted right next to it), and while it helped me dial-in my 1850 Holley, I will freely admit that I stole some of the initial settings (jets, etc) from Roadkill's "Tater Truck" episode to get me in the ballpark, as their 390 seems to be very similar to mine.