The 1268 (bottom gasket in pic) is thicker, and the ports are slightly smaller both length- and width-wise. It also provides more surface area. This is the gasket the shop used when welding my intake, and they liked the way it lined up.
The 1203 (top gasket in pic) is what some others are using. It really comes down to personal preference in my opinion, and how ported you are making you intake/heads.
The difference in thickness is subtle, but noticeable. The 1268 is a .9, and the 1203 is a .6. I believe that is in mm, but not positive. I don't have the port size measurement differences handy, but can post them if anyone really wants to know.
the red lines on my intake is a trace of the 1268 gasket alignment. That is basically how much material i will be grinding down off the intake to help flow.
Just thought i'd share the pic/info.
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