If someone cut the rebound spring as short as you say it would basically fall into the gun with no compression. If the gun was functioning with a spring that short there has to be a spacer in the rebound slide to give it some compression. If you installed a standard spring with he spacer in place I would expect that the gun could not be cocked because the spring would coil-bind and prevent full travel of the rebound slide. Some way you have to get the spacer out of the rebound slide.
Depending on how a spacer was installed, and what it is made of, it may be difficult to remove. You may have to drill it out.
The hand should have a slight flat on the end. S&Ws do not lock on the end of the hand like Colts, they depend on the thickness of the hand. When close to full carry-up the hand bypasses the ratchet lug and bears on the side of the lug. The failure to carry-up can be repaired with a new oversize (thicker) hand, slightly peening the ratchet lugs to spread them slightly, or slightly bending the hand. Unless you really understand the S&W lockwork, and obviously you do not, none of these fixes are something you should attempt as you can do a lot of damage really quickly. David Chicoine
www.oldwestgunsmith.com would be a good place to start. There are very few gunsmiths that can be trusted to repair either S&W or Colt double-action revolvers, unfortunately.
A good place to start would be to buy a copy of Jerry Kuhnhausen's
"The Smith & Wesson Revolver, a Shop Manual". You can buy it from many on-line booksellers, Midway, Brownell's, etc.