I recently wanted to put a Gates HD belt in my C5 Corvette. Standard LS1, with a Magnuson MP112 unit sitting on top, and an ECS tensioner which shouldn't actually make a difference but who knows.

The standard belt recommended for the application is: K061045, or 6PK2652; size is 13/16" x 105" outer circumference, or 20mm x 2666mm outer circumference, 6-rib.

There's no Gates HD belt with that precise size. I can however confirm that the Gates K061058HD does fit properly. The length difference is within spec for what the tensioner will allow.

Bonus fact: the AC belt is a confirmed fit as well: Gates K040420 Multi V-Groove Belt. It's not an HD belt, but it's plug and play.