Some of those rear pull-offs have a dual setup. there's two slotted links coming out of the plunger on the pull-off. they have two links, one goes into the choke mechanism, the other connects directly to the secondary air valve. (big flapper on top) I personally prefer the front pull-off mostly because that's how most of them are.
Those who know me know I've more than just a few Qs, one of the best I've ever had was a later style 13 screw top 800CFM with a rear pull-off. Thing was like EFI, instant response, good manners cold and hot. Got 14-15 around town, 20 on the hiway. This was a 406 roller, aluminum heads, Eddie Perf RPM Q-jet, prepped HEI, 200-4R, 3.73. ran 131MPH for 10 miles across a new fwy here in the desert.
Tom Terrific or Terrible Tom, depending on the phase of the moon, passing cosmic rays or other factors not fully understood except by my wife.