When I built my 1850 years ago using C.B. stuff, I had to use the 88mm stroker piston on a 76mm shaft. I don't know about the 74mm crank.
     Your 74mm will have a 5mm gain over the 69mm stock crank and I suppose they will want you to do some serious cyl. decking do to the stock wrist pin location on your 90.5 cyl.  You better have the stuff to do this and get it right and I mean right.
      You better rethink about using duel Zeniths DINX , if this was your plan.  Porche tried this on some of the 356's and found that they blew more gas out of the top of the carbs than was going in much less being a hassel to keep adjusted.  Porche " Normal"  ran the Zenith as a single and did pretty good with it.  They finaly went Solox.
       Are you going for a new case ? It just money.  
       Good Luck :roll:  :roll:  :roll:

------- Just when I thought there was hope.  Oh well !!! :roll:  :roll:

Its always better to be messed with than messed on and just remember you will never be able to out-mess me. I just love reformed "whipper- snappers"   Do-Dar, Do-Dar !! :lol:  :lol:

The words  Mess or Messing is a generic term for the benefit of those who seem to have freaky things that manifest themselves without having a clue to know what happened or why.   Example: I don't what happened ,but this oil pump is "Messing" with me.
      The A versus B Piston ?   I don't have a clue , I haven't "Messed" with anything like that :lol:  :lol: