i'm with sixnut completely,
crank, cam, bore, valve etc etc wear or issues, would be notable in more ways than just lack of oomph, including guage indication there would be noises, potential smoke and smells etc etc,
and so fresh from a rebuild, with good oil pressure, good compression etc, i think you can safely discount a mechanical issue,
leaving, as sixnut stated, fueling or ignition.
if it was a fueling thing, i'd start at the pump, filters and lines, then once proven reliable up to the carbs, (which i believe have been rebuilt, new gaskets etc?) i'd start with accelerator pump diaphragm and valve, are the pump galleries correctly clear and asembled?
then get in a little further with the airline, get them jets outs and the carbs throroughly cleaned through and carefully rebuilt again, double check for a nipped gasket along the way.
has the float height been changed at all? double check that once down there, plus were the needle valves repalced within the rebuild / service
if you can prove all that is good, you should be able to eliminate the fuel side of things.
as for ignition, you've set the timing correctly at idle i beleive, so that should be good enough for standard performance,
what type of distributor do you have? and is the advancing working?
you should still be able to basicly check this with the timing light, as you pick the revs up the flywheel marks you see at idle should go scurrying off pregressivley out of view, that should be an indicator at a very basic level that the advance device is working.
i note that you have new leads and plugs, so that should be good, what about the dizzy cap and rotor arm and main coil?
and, please don't take me as a condescending arriss, but the plug leads are in correct position yes,
its easy enough to get wrong, i've done it myself and still have to double check things like that to this day, so i'm really not trying to take the mick!
but starting, eventually, and running, but poorly, it could very easily be something as daft as that.
the above would be what i would do, and i hope you find something easily and silly, as it often is!
best of luck