Propshaft length - the complete story

After some discussions with Westfield (who weren't very helpful) and some posting on the FM forum (which was very helpful - thanks Keith!) I now know enough about the MX-5 diff/engine combinations over the years to make me a real bore at parties.

Quoted from Keith:
"The diff was changed in 1994 when the 1.8 came out. We never got the 1994-97 1.6 in the US, but it makes sense that the larger 1.8 unit was used for ease of production. That looks like one to me.

The "stub axles" you've seen in other pictures simply slot in. They're half of a two-piece halfshaft - would that make them quarter shafts? In 1996, Mazda went to a one-piece halfshaft. There's no functional difference but the one-piece units offer a bit more clearance. Mazda never used a one-piece halfshaft with the smaller early diff, so that would support this being what is often referred to as a "1.8 diff" by US owners."

The result of this is I need to have the propshaft shortened from the current 555mm to the 505mm measurement the build manual states for a "1.8" diff. This also makes sense as the engine was 20mm off + you need ~20mm of play (so I've been told!).