I can echo what Jay says about coil breaking down when hot. One of my 70's Chevys recently would start up and run fine at first but when things heated up it would would start acting up especially at low RPM. I too initially thought I had a carb problem but turned out to be the coil.
I removed the second set of throttle butterflies on my 68 with Strombergs and it runs a lot better with out them. MUCH better throttle response for me. I pulled the carbs off as a set and removed the two screws that hold each butterfly plate in the shaft and withdrew the plates. I left everything else intact.
David Barnes
68 E-Type FHC