For the gaskets one says "D-shaped Center with Oval End Ports" and the other just says "D" port. There are only one size "D" port as far as I know, they are either round ports, pre-1970 (with the exception of the Ram Air heads) or "D" ports 1970-up. As far as header go, in my opinion they are not worth the hassle for 15-25 HP that you might gain from them. When I did my build I could not get any make headers to fit into my engine bay, the passengers side is ok but the drivers side they all hit on the steering column and A-arm, so you have to notch or bang them in with a hammer in order to fit. Plus my collector gaskets constantly leaked and they hang lower than factory headers of course, so when you go over a big speed bump they could hit and then bend the collector flange which happened to me a few times. I swapped to the factory headers like the ones you have there back about 20 years ago and never had to change a manifold gasket or had a leak. Headers in my opinion do not justify the 15-25 hp that you gain vs. the leaks and problems that I had with them.