5208s sorry I'd didn't see thus earlier or could have rattled that off top of my head. Much experience with these on a 340 head :BangHead: as in the ports are too small and won't seal. The primaries are 1 5/8 small and the collectors are 2.5" iirc. They fit 273/318s great. Must use a port plate for larger port heads. They will leak out the bottom on a large port head. ~$500 used all day!