Go for the ferro concepts slingster if you got the cash, very very nice sling and has a fast tensioner on it so you can pull the slack out of the sling when you need to do something like climb up a ladder and then loosen it off when you need to pew again.
That's a completely different type of helmet made by a company called Team Wendy, Ops Core haven't changed the design of their rails at all.
There are adapters for Team Wendy rails, but as far as I know only real steel ones so expect to pay a bit of a premium.