Is the vacuum advance hooked up?

Does it slowly die (struggles to run) or is it a pretty quick thing?

Do you have a vacuum guage?

That is a lot of carb for that motor - but that is not the problem... but has the carb been tuned for the motor?

Was the other truck in driving condition? I.E. are you sure it was not dying if the clutch was fully disengaged at idle?

Are you sure the distributor was set at TDC?