fuel leak

[jonnymel]

Help Please
I am trying to get my Truck running for this coming weekend .....for the bride and groom to leave the church in .
I have a 1960 GMC 454 with a holley 750 carb. I have done away with the crappy fuel cell that was in it to make room for the exhuast and fabricated a bracket for an older style corvette tank mounted in the bed behind the cab . The tank will be mounted on this bracket and inside an antique chest. the tank is mounted about 5 inches above the bed floor.
After a quick drive and return home to make some adjustments ( new motor and tranny). the next morning I noticed fuel had puddled on the top of the intake...i pulled the carb off and there was more fuel inside the intake.....i pulled the plugs and fuel poured out of one of the cylinders . I drained the oil and am ready to start again.

have i made a mistake in mounting the tank where i did ? i can install a fuel shut off at the tank but shouldnt the carb stop the gravity feed of fuel from entering the engine ?
Any help would be greatly appreciated ....i have little to no experience working on carbs......( this was a freshly rebuilt carb )