USGI slings all look standard length. To be honest, I've never seen any that were extra long.
Boonie Packer has a loop that will go over the front portion of the larger M4 handguards. They also fit on RIS/RAS equipped with panels. The loop has a piece that needs to attach to the conventional front sling swivel. The part for the rear attachment is similar, but need to go thru the slot in the stock just below the buffer tube. I think it is a BP-52.