I just cut the top off my 50 and installed a 54 top. About 6 hours of cutting and trimming yesterday, and another 6 hours welding today. Next will be to sandblast the welds and start the body work.
http://i82.photobucket.com/albums/j279/snkbte/Chevy%20Pickup/Mytruck1.jpg

http://i82.photobucket.com/albums/j279/snkbte/Chevy%20Pickup/A50to54conversion.jpg