I have the Magnum 91 and I have yet to start it.  I frantically dug out the manuel and read it comparing your postings.  Yep capn, I see exactly what you were reading.  My bet is the 70 and 91 are different in displacement only.  Not glad you are having a tough time of it, but glad you started this thread.  All the info I can get before starting mine is a big help.  Probably gonna be about 2 more weeks before I fire mine up.  Keep us posted on your progress.