[jgpnashville]

Yes, the truck started when I got it home, but after some more thought, I capped the PCV/Power Brake vacuum line on the throttle body side of the Holley carb, since the truck doesn't have power brakes or a PCV line. This means that the timed spark vacuum port under the choke is capped, as is the power brake/PCV vacuum. Doing this has helped it idle much better, but maybe the timed spark vacuum and the full manifold vacuum lines should both be connected via tee to the vacuum line from the distributor. I'll try that next.

I bought a collection of throttle return springs from O'Reilly's and installed one of the lighter springs, which seems to provide enough tension to return the throttle back closed. The fuel level in the bowl seems to be about right - it was right at the edge of the screw hole on the side, but I haven't measured it after cranking with no throttle. It is worth mentioning that the truck starts so much better when cold with the Holley vs the Stromberg - I rarely have to touch the choke, but it also hasn't been much below 50 degrees F, either.
The only issue now is the engine has a tendency to die when coming to a stop, such as approaching a stop sign or traffic light. It restarts easily, but something isn't right with fuel delivery. I'm wondering if the engine is being flooded since the Holley 4412 has the original jets in it and may be over-providing fuel to an engine such as the 305e. Once when it died at a light, I smelled gas, so that has me wondering. It's worth noting that when I put the clutch in to coast toward a light, if I give it some throttle, the engine won't die.
I haven't tested fuel pressure with a gauge and tee, since I don't own one, but perhaps that's worth buying for this issue, if after connecting the timed spark vacuum port with a tee doesn't improve the way it runs when coming to a stop.

Thanks for all your suggestions. The truck is coming along and while the manual steering takes some getting used to, as does the SM420 shifter, notably downshifting from 3rd to 2nd seems touchy and a bit hard to find 2nd consistently, it's going to be a great vehicle.