The #136 would work with either of the two stocks. It mounts using the sling slot at the top of the stock. The #135 is for standard handguards, not the fatter m4. If you are going to use the side swivels on the front of your rifles I would recommend the #137. It uses the swivels instead of mounting to the handguards.
Just to make things more confusing you could also use the #200 sling which includes adapters for the M4/A2/M203 setups. This is kinda nice to have if you ever switch furniture, or move the sling to a different AR.
I stock most of the CQB slings and try to offer them at the best price. $36.95 plus $5 shipping USPS priority with delivery confirmation. The #200 are $38.95. Usually ship the same day I receive payment. Money order/paypal with no fee.
Let me know if you have any questions.
Thanks
Adam