I just purchased a 64 C10 truck with long be fleetside.  It has a 283 and 3 speed on column. Their is a tag on the driver door jam, what is it?  Serial number or cab number?  Also, is the 283 3-spd standard equipment on this truck?  

Find the vin# on the dash next to the windsheld. Go to www.lmctruck.com and they have what it stands for right after the index. It should be on the title as well. Most of them old trucks had stright shift tranys. If the shifter is on the column it standerd equipment. Not sure about the tag on the door could be the vin number. LMC will tell you were the vin# is located.  

What would be a good four speed transmission to put behind this 283 engine.  I plan to increase the HP and performance of the engine and would like a good four speed with a floor shifter.  What was the gears in the rear axle?  Somewhere I read it came standard with a 3.73.  

I think you are right on the standard gears. with over drive you want any were from 3:73 to 3:25, 3:50 is what most run. With 4 speed you want from 3:50 to 3:00. Most of the newer built trucks and cars are doing 5 speeds like what S10 run. That would be my choice if I ran a staeight stick.