@Ricko1966 does have a point about fuel pressure. If you had to much fuel before the rebuild and you still do.... But before you didn't have gas spilling out everywhere now you do. So it's clearly worse.
I would do exactly as Rick has suggested cut the fuel supply off. Lower the floats, all the way that's by loosening the screw and turning the nut all the way down. Fire up the truck and run it until it stalls. This will drain the primary bowl for sure, the secondaries might still have fuel in them, but you might be able to get creative to get that out or at least a bit lower like snapping the throttle a few times to get them to open and use at least some of the fuel out it.
Then turn the fuel supply back on and crank the truck. It should refuse to start, or if it does start the fuel level should be well below the sight plug. Assuming it refused to start, working with the primary side only slowly increase the amount, maybe 1/4 or 1/2 turn of the nut at a time until it starts. Once it's running set both floats the normal way with the engine running. Ok, so if it floods gas everywhere when the nut is turned all the way in, I'd suggest that you pull the primary float bowl, or possibly both float bowls and post good detailed pictures. Maybe one of us will spot the problem in the pictures.
Additional note: Rebuilding carburetors is not particularly hard, even Q-jets which some people find daunting. The main things
#1 cleanliness, even the smallest spec of dirt or sometimes even lint off a rag can plug a passage or keep a float from sealing properly.
#2. It is very helpful to have compressed air so you can blow out passages, and dry off parts you have cleaned. As well a little blast of air can insure there is no dirt on something before reassembly. If compressed air is not available a can of air, like the stuff used for cleaning computer parts will work.
#3. Measuring out and setting adjustments correctly the first time.
#4. Knowing how to disassemble and reassemble correctly, since we all carry a smart phone in our pockets there really is not excuse for not knowing how to reassemble something we have taken apart. I remember back in the day drawing out how parts would go back together when rebuilding a carb I didn't know well.
#5. Knowing what to do when you have rebuilt a carburetor and something doesn't work right after.
#6. It is EXTREMELY helpful to be able to learn the art of carburetor overhaul from someone in person that can correct you or help you as you go along.
If all else fails for $249 you can purchase a rebuilt Edlebrock 1406 for national carburetors. Now I'd really like you to succeed with this rebuild, and I think your very close if you can get this flooding issue taken care of I just wanted you to know there is a way out if there comes a point that you have had enough. Keep in mind you'll at least need an adaptor if you decide to switch.
