The primary advantage to a shorter barrelled shotgun isn't in pattern size or swing speed. It has to do with moving with the shotgun. When a stage calls for the shotgun to be shot through 3 different windows, the long barrel hampers getting in and out of said windows in a timely manner. It's a similar issue to getting a long pistol in and out of a holster. The other issue is that the full fixed choke, particularly in a gun that was designed before the use of plastic power pistons was common, tends to throw a pattern of about the same size as a rifle bullet. the old style full choke, combined with modern ammunition produces an effect similar to a super duper extra full. Since we're shooting in a hurry, at targets between 8 and 20 yards, rather than birds at fifty, such a pattern is sub optimal, to say the least.
Anyhow, I'd say that about 75-80% of '97 shooters use one that's been cut down, or a norinco that was built that way.
If avoiding the norks, and not having to desecrate a good original is your goal, I'd suggest buying one that's already been hacked, tubed, and tuned for SASS. they generally run about 5-600 bucks on the sass wire.
One thing about SASS, though is although it can be satisfying to shoot the originals, it's danged hard on the originals. Guns get shot fast, slammed around, slamfired, and occasionally dropped.
One of the saddest things I ever saw at a SASS match was a fellow who always prided himself on shooting originals, and doing so competitively. The stage required that pistols be staged on the table, rather than being holstered. When he slammed his second pistol down, it inadvertantly landed on top of his rifle. The end result was that the circa 1891 Mother of Pearl grip got busted off of the 1884 Colt SAA, which then exposed the steel of the grip frame. Said steel promptly gouged a four inch chunk in the barrel of his circa 1884 Model '73. Poor guy literally cried.
~~~Mat, aka Jerkline Jesse