On an HK33 with similar handguard length, I like the Trijicon HK-specific mount and a TA01 ACOG. This is a channel mount for the ACOG and uses feet to grab the claw attachment points. For your short(er) barrel .308 ballistics, the .223 reticle will be close enough for minute-of-tin-can, and you can range it more accurately if needed.
This setup of the TA01 on my 16" barrel HK33 is a tack driver due to the solidity of the mounting system. There's no way to get around stacking them with this setup unless you have a rail welded to the top of the gun,