The front spindle is where the front wheel bearings and wheel / rotor hub is located. On a 2 wheel drive auto, the spindle is the point were the front ball joints are connected to the A-Arms which connect to the frame. On a 4 wheel drive auto, the spindle sits in bearings inside the front steering knuckle which the ball joints attach the A-Arms to the frame. Do you mean the front axle for the 4x4 system ? The front axle shaft has nothing to do with installing the transmission into the truck as long as you marked everything from both sides of the couplings (the driveshaft side and the flange for the transfer case side) at the transfer case before dis-assembly so that you don't re-install the driveline "out of phase" which could cause problems later.
If the transmission torque converter (bell housing area) is not fitting up to the flex plate correctly, then just give the trans torque converter a spin or check to see if the trans housing (bell housing) is not aligned with the locating pins on the engine block. If for some reason you did not mark the driveshaft's and transfer case flanges at disassembly, sometimes looking for matching dirt or scar marks will assist in correct installation so that you don't get an "out of phase" situation.
IF YOU are talking about the primary shaft coming out of the transmission which the torque converter slips on to, no it wont spin with just your hand without the transmission being shifted into neutral and it might not even then, as it is solidly connected to the inner working of the transmission and is also the output shaft . Add a quart of fluid to the "dry" torque converter and slowly spin the torque converter on to the primary shaft until it sits on (or in) all the way, then use wire, heavy string or a coat hanger to hold it in place until the last inch from the engine flex plate. Even installed on the primary input shaft, the torque converter should spin freely.