The carb kit directions should show you how to set the float level properly. If they don't, look up your carb online and see if you can find the adjustments manual.
Timing - if you set the timing too far off the engine can be very hard to crank. The battery might not even be able to turn it over. The engine can rattle or knock or spit back through the carburetor. I wouldn't fiddle with the timing until you get the motor running. Make sure you use a timing light (borrow one from a friend if you don't have one) and set it to factory specs. You can fiddle with changing the timing later - after you've got the truck back together and you want to test some things to see if you get better performance.
Timing can either be advanced, neutral or retarded. Advanced means firing earlier in the compression cycle. Retarded means firing later in the compression cycle or even after the piston has reached TDC. Too much advance and too much retardation can both cause lots of problems, even going so far as to mechanically damage the engine.
All points distributors have mechanical advance weights that advance the timing as the RPMs increase. This is because there is a delay between the time the spark plug fires and the time the fuel mixture fully ignites. As the RPMs increase, the piston reaches TDC faster, so the spark plug has to fire sooner in order for the engine to run properly.
If you think about that, it should tell you something about timing. You need the fuel to fully ignite just as the piston reaches TDC. Too soon and the fuel explosion will be pushing against the piston as it is still rising, fighting against the movement of the piston, reducing power and potentially damaging the rods, pistons and/or bearings. Too late and you lose power because the piston is already going down, increasing the total volume of the compression chamber and therefore reducing compression (which reduces power.)
For most older motors the timing is set somewhere between TDC and 10 degrees advanced. The sweet spot is where the fuel has fully ignited and is beginning its explosion at the exact moment when the piston reaches TDC and is ready to move downward and the compression chamber is at its smallest possible volume. You can imagine that with all the variables involved (weight of the pistons and rods), friction in the engine, condition of the ignition wiring system, etc., etc., the perfect timing for each motor will be similar but not exactly the same. The factory selects a timing setting that will work well for all motors, but your motor might work better with another degree of advance or a degree or two less advance.
