I can't see the pictures from Isayeret, but are you sure that you saw a Colt Model 633? That's a 9x19mm caliber sub machine gun based on the Colt Commando, which probably never found its way to ZAHAL.
The original American "mekutzrar" is the Model 607/608/609/610, with a very short 10" barrel and a very long, 3 to 4" flash-hider. This family, that became known as the "Colt Commando", was introduced sometime in the mid to late 60's... don't know when they showed up in ZAHAL (very curious to know this actually). The 10" barrel was abandoned in later designs because it was found to be inadequate, but ZAHAL's workshops never got the memo apparently.
Also, FYI, the original "mekutzar" is the Colt Model 653, it was first made in 1973. That's the one with the M16A1 type receiver/sights and the 14.5" barrel, with a "normal" looking flash-hider. People like to call this rifle "CAR15" and some sources claim that ZAHAL already had those in service in the Yom Kippur War, pretty hard to believe. Does anyone know when it was actually first used by ZAHAL?
Of course there's also the "commando" version of the M4, the Model 733, with an 11.5" barrel and a normal M4-style flash-hider/compensator. While I'm at it, the M4 itself is the Colt Model 720, the full auto version is the 727, and the M4A1 is the Model 927.
There's a very comprehensive run down of the M16 family right here (scroll down to the 2nd table for the most useful information, about the military versions):
http://www.biggerhammer.net/ar15/variants