the keywork looks very 6M-ish - the left hand little finger cluster is certainly similar to mine... there were a lot of 'transitional' Conn's that have features of both the 6M and the New Wonder. The neck has an underslung octave key but no microtuner, which is no great loss. Yours doesn't seem to have as many tiny grub screws as mine, but they're the thing that repairers moan about the most...
there's more info here -
http://www.saxpics.com/?v=mod&modID=45
The Nickel plated keywork and lack of microtuner and locking screws would indicate that it's probably from the mid to late 50's - the serial number will give you a more accurate date
The difference between a 6M and Comm II? Well, I've never played a Comm II alto, but I've got a 6M and a Martin Indiana and Medallist. Tonally, the Conn is clearer, purer and a bit brighter, but with a fat low end and if you know how to use your embouchure can go from a whisper to a roar, whereas Martins have that typical plummy lower midrange and a softer top end. My Conn is very responsive, it really gives out what you put into it, but as a result it's more revealing of your shortcomings. Whereas the Martins feel a little more relaxed and more forgiving of sloppy playing. A Martin will also roar and scream, but will always have that sweetness - the Conn can be as sweet or sour as you want it to be. The altissimo and multiphonic fingerings are different on the Conn, but it really has the edge over the Martins in that department.
If they were guitars, the Martin would be a vintage semi acoustic and the Conn a Les Paul Gold Top with P90's
The body tube on the Conn is noticeably narrower than my Martins, but I'm not sure what effect that has. The Conn's a bit fussy over mouthpieces, but it loves my Lawton BB, so modern mouthpieces will play on these things. I've tried vintage mouthpieces, but she's not amused...
Whoever designed the left hand little finger cluster on the 6M was a genius - every sax should be this way, far easier than that modern Yamaha design that's ubiquitous these days.
You may need some rubber palm key risers and the thumb hook is a bit uncomfortable, so a rubber thumb cushion is a good idea. Some folks have the strap ring moved to help it balance better, but it's not intolerable
hope you like your Conn as much as I like mine.... happy blowing!!!