You will never be able to have exactly what you want in a semi-auto rifle. The M16A1 you describe sounds like it was built on Contract 508 "one time buy" receiver, manufactured 1964-67. This would have a pivot pin retaining boss, but no mag fence, no reinforcements of the buffer housing, and no radius on the pivot pin lugs. This receiver was never, to my knowledge, used for other than select-fire M16's.
The lower receivers you have available are the SP1 (no pivot pin retaining boss, requires an adapter pin to work with standard uppers) or the current A2 models (from Colt or anyone else, they all will have radiused pivot pin lugs, reinforced buffer housing and a mag fence). As others have pointed out, the upper receiver assembly should not be difficult to find, but you are a little handicapped on the lower.