Couldn't find a forum but did look a bit more into the 123 manual- found the list of mappings relate to the various types of dizzy (above) - just need to work out which 005 my van had originally!
Look at the remark next to curve 0 Let's face it, aircoolers of any description aren't exactly Cosworth engines...
The forum doesn't seem to exist any more, but I recall curve 0 was the suggestion for a type 4. I'd doubt you'd lose much with the default curve. As perspective, your nan's Nissan Micra has more power than a 2 litre type 4 PS Set it to curve 2 (with double-sparking) if you're feeling adventurous...