Andyman,
Yes, that transmission, if it has the torque-tube fitting at the rear, will work on your truck. No modifications would be necessary, and it is a fairly easy swap (although. the 4-speed is at least twice as heavy to lift).
You will need a 4-speed 1/2 ton u-joint. If the '49 was a 1/2 ton, that u-joint will work.
If you do not mind my asking, why do you want the 4-speed? Is your three speed giving you problems?
Thanks, Tim
