If you stand in front of the truck and imagine looking down at the engine, the rotor should be at 9 o'clock when the number one cylinder (the front cylinder) is at TDC of the compression stroke. Four stroke engines have two cycles of the piston for each power stroke; compression (moving up), ignition or power (moving down), exhaust (moving up again) and return (moving down again.) You want the spark plug to fire just slightly ahead of TDC so that as the flame front grows and begins to expand, the piston has reached TDC and is in a position to be pushed downward.
Your goal isn't to achieve perfection during the mechanical setup. It's to get the rotor in the right location generally. Perfecting it comes when you move the distributor clockwise or counterclockwise to set the timing according to the manufacturer's specifications.
The precise positioning of the rotor is done with a timing light. From your description it sounds as though the rotor is where it should be, so the rest is timing. When you loosen the clamp that holds the distributor in place you can rotate the distributor clockwise and counterclockwise. That's how you adjust the timing.
Yes, the cylinders are numbered in order from the front on a six cylinder engine. And yes, you should be able to turn an engine over with the plugs out by putting a socket wrench on the harmonic balancer pully nut. Actually, you should be able to turn it over with the plugs in, unless it was just rebuilt and it's a high compression engine.
It wouldn't be surprising for the inside of the manifold to be wet with gas, but there shouldn't be any gas standing in the manifold (like puddles). When a carburetor is working correctly, it sends a mist of gas into the manifold, not droplets (ideally - they're never perfect). That mist should be taken in (for the most part) by the cylinders and not left in the manifold, even if the engine isn't firing. The spark plugs would be wet from the gas (if the motor isn't firing), but the manifold should not have puddles in it.
Float level is critical, so make sure you follow the instructions in your kit precisely. Also verify that the float moves freely and does not hang on anything. And make sure that the inlet valve is seating correctly and closing correctly when the float reaches its top position.
