Produced between 1970 and 1972. 

The rotating head on a normal Mitchell 300 reel turns clockwise, when viewed from the back of the reel. Since most people are right handed, this presents two problems for the tournament caster: First, when casting for accuracy, most competitors use the forefinger, during the cast, on the rim of the spool to slow the cast. This does not work well with a right forefinger because the line is coming off the spool in the wrong direction. Secondly, It is difficult for the right hander to lift the line with his finger to catch it with the pick-up. 

Prior to the advent of this reel, a lot of guys used the right hand version, the 301, because it eliminated this problem.

The rotating head on these competition reels turns counter clockwise (when viewed from the back of the reel). This was accomplished by using a 301 rotating head, and an intermediate gear to cause the head to rotate clockwise.

There were several different spools manufactured for these reels. This particular spool is a two stage conic design. The Manual pickup is double adjustable. The front (small part) of the spool is used to hand wind a shocker line. The back (large part) of the spool on this particular reel has machined ridges. I think it had thread wrapped on it and a previous owner took it off.  I say this because of the Patina on the front part of the spool and none on the back.  Quite often, a fine thread would be wound on this part of the spool.  This was usually done by the owner of the reel. Although this particular spool surface is ridged, if the spool surface were smooth, the casting line would have slipped on the spool because of the cone shape. Winding thread on this part of the spool helps prevent the problem.

Also, it has a "lock down nut" on the handle shaft to keep it from turning while casting. 

Only 17 of these reels are know to exist today. Considered "Super Rare" in the community of Mitchell collectors.