Lean condition under light acceleration

You very well may be right that at the beginning of the incline its still on the transfers. 30 mph could be, 60 almost certainly not. In between I don't know - especially with a spreadbore which oguht to be on the mains sooner. ????

As far as the rod being the restriction, IF its on the transfer/idle circuit I think its not.
I've not measured Thermoquad restrictions but generally it seems that Carters, Webers, Holleys the IFR restriction is signifcantly smaller than the main restriction. The rule of thumb for two restrictions in series is if one has four times the area of the other, the large one has essentially no effect on the flow.

This isn't the best comparison but the only spreadbore I have pinned, which is a Holley.
Primary IFR .028 " dia => .0006 sq inches
Original Jet #62 .061" dia => .0029 sq inches

The Carter has to be in the same ballpark. The engine is consuming about the same air regardless of carb. The restriction for main system has to be sized so the same amount of fuel. The difference in main systems with a Holley 6213 spreadbore versus the Carter T-quad shouldn't be that much as both use small primary venturis and throttles. The T-quad's booster design should create more signal and I don't know about the air bleeds (or one year a solid fuel circuit was used?) - so its not quite apples to apples but its not going to be orders of magnitude different either.

Now there is one more little monkey wrench in the restriction relationship. Carter's 'low speed circuit' has a two air bleeds and two fuel restrictions.
Discussed a little on page 4 here Carter AFB-AVS Service Manual
And Tuner gives his take on them in a sidetrack here 3310 and Fuel mileage