340/mag360 exhaust manifolds

I noticed in some of your pictures you have some center dump manifolds but you dont mention them much, I am on this site because my youngest son has a Duster but MY project is a 56 Dodge truck on a 83 Dodge truck frame, its still going together and I am just trying to figure out my exhaust now, what I need is center dump on both sides, what I have got now is d/s from a "A" body 69/70 318 and p/s from a 80 Dodge truck 318 but they are the smaller exit, also I tried the later, (80,s) 318 center dump on the d/s of the truck but it is two thick at the end and touches the fire wall, ( remember this is a street rod), sooo.. my question, is the center dump you have a large diameter exit and tight, ( short bolt ) at the ends? , thanks