I know this is a couple year old post, but I wanted to point out a potential issue when using the 1255s for anyone who stumbles on this thread like I did...
After a lot of research on what to use on my project, I bought a set of 1255s because it seemed like the logical choice when evaluating the failure modes of intake gaskets on the vortecs. I had also bought a Mahle complete gasket set for the rest of the engine that had the composite intake gaskets.
As I was gluing the gaskets to the heads using studs to line everything up, I noticed that the "center ports" on the manifold (no idea what the purpose is on them other than oil drain back and potential oil cooling in the valley) were lining up slightly above the gasket. I applied gaskesinch to the intake to confirm my suspicions ( used glue as layout fluid). It appeared that the single opening side was right at the top of the gasket, and the side with 2 were just proud by .5 to 1mm.
Not sure if these gaskets have had any revisions lately, but they would most likely allowed a vacuum leak in my application once torqued. I've seen many accounts across various forums complaining of a whistle and leak on vortecs discovered by vacuum tests...I suspect this could be a culprit of a few. May not be an issue on all due to manifold production variation, etc., but its something to look out for. Seems like felpro could just raise that top bar 1/8" and would likely be okay. I had a spare manifold so I snagged a few pics to show. Hope this might help someone.