crossboss - I'm a little "fuzzy" on details... It appears UR-18 was an individual Runner Dominator Flanged Manifold, and then there was the UR-11 "piece" which went on top an made a plenum area above the Individual Runner UR-18... But this is only from looking at pictures, not actual on-hand parts. I also do not have a period catalog to look at for information. Also have seen pictures of one that appears shorter than the UR-18, but don't know if it was modified or what.