The 4150 Holley carbs with no rear metering blocks with screw in jets like the double pumper use won't work in line, the single inlet vacuum secondary carbs like the list # 1849 and 1850 will fit in line They don't have the thick rear metering block, they use the thin rear metering plates so the rear float bowls don't stick out as far as the other carbs do with the thicker metering blocks
I've use them on several motors including other than Mopars, don't tell on me though
Running the carbs mounted in line with no progressive linkage makes those motor really responsive and that helps make more power