I think I can answer this one, although not in detail. Yes, there is a difference in the block to bellhousing bolt pattern between the 235 and the 283/327. The series of inline 6's after 1962 did share the same bellhousing bolt pattern as the V8's, as I understand it.
Others with more knowledge will certainly chime in. I just caught this one as I am about to announce a mea culpa.
