Been using a KAC qd sight tower mounted side sling adapter.  Happy with that BUT I cannot use a Surefire 600 w/sight tower light mount that I picked up cheap.  So, I'm going to have to go with something mounted lower, on the barrel, but would still like the qd button arrangement offered by KAC if possible, or something equally well made, and a good source to purchase same.  You guys here have saved me so much time and money spent in mistakes in the past.  Thanks in advance.

Have you looked at our (KAC) MWS Sling Mount Adapter that mounts to any of the RIS or RAS rails?

I agree. If you have rails up front use the KAC mount on the rails. I have one on my M4 and love it. I have the tower mount on my 20".

If you want it all on the sight tower then try the SLIC made by GG&G. It mounts the light on one side and the sling on the other. It is not a QD setup though.

Surefire does make a mount that holds the light parallel with the barrel - mounts to the barrel - and would not interfere with your sight tower sling setup. Sorry I don't know the model number.

Thanks guys.  I have my KAC RAS on another upper with the KAC side sling rail adapter (love my RAS).  However, this setup is my "lightweight" and I intend to keep it as no frills as possible.  Already have a WFM mount that will take my Surefire 600, but want to also be able to use my Surefire 600 on my no rails model.  Already have the Surefire front sight mount, and it would be cheaper to buy a barrel mount side sling adapter (as I guess is on the M4) than the Surefire barrel adapter.  I guess I simply need  the side adapter that mounts in that slot on the barrel under the front sight tower.  My barrel is an M4 14.5.  So, what adapter do I need and from whom?   Thanks for your help.

For your "lightweight set-up" where you don't want to change-out the handguards, I'd go for a Single Point Sling and give up on what sounds like the 3-point sling your using.
All kinds of guys offer single point attachment hardware for the small of the stock.

Thanks Coldblue.  I'm somewhat hooked on the three point arrangement right now having only recently discovered it.  I'm slow to new technologies as I am to movies.  By the time it's gone from the theatre for about a year or so, I'll rent it ;)