Well Willi
Elmer Keith is well revered in handgun circles. His contributions are legendary. Oft overlooked though, is the fact he was actually fairly stupid. He blew up quite a few SAA and other guns in his untrained experiments.
Your new cylinder and barrel might well stand the increased chamber pressure created by those Keith loads. However, if we are talking about an original Model P, as mentioned by Abilene, you may see some frame distortion.
A Uberti SA on the other hand, is made from much sterner stuff than an original pre 1896 Colt. With a .44 Caliber Cylinder and Barrel it may well stand some really impressive (stupid) load levels. Your Hands, your Eyes, and they don't make replacements.
Play Safe Out There
PS: If you wanted to play Dirty Harry, Why didn't you just source up a 44 Magnum?