I will try to post my questions here as well, since the forum seems quite dead.
It seems i have solved some of the problems during the weekend but some remain.
My setup is nailhead 401 1962 with sp400-1966.

Q3: the switch pitch problem remains./see tranny etc.
Q4: also is there only one correct way to mount the flexplate? How should it be mounted?
I read an article on buickstreet.com from hot rod magazine that said that it was a common problem mounting the flexplate wrong when reassemblying the nailhead? According to the article there was six ways to mount it but only one right way.

Best regards Rob