Timing setting Pinasco 177 Aluminium kit

I decided to take the plunge got a Pinasco aluminium 177 kit and SI 24/24 carb for my 2007 px125. I'll be running this with my SIP Road exhaust.

Any ideas on what the timing setting should be… 18° or 21°?

Pinasco instructions say set to 'IT' on the stator, does that mean it's OK to leave it as is ('IT' would be 18deg BTDC on the later models like mine, wouldn't it?).

Beedspeed reckon it should be set at 20-21deg but ALSO at 'IT' setting (http://beedspeed.com/html-pages/IgnitionTiming.htm) I'm wondering whether this is for older vespas.