will it start?

Well to cut a long story short.... yes it does! :-)
Of course it does.  I shouldnt have been surprised really - Vespas - they're not rocket science!

But to tell the long story....
Its saturday, which means I can comfortably take the whole day to myself in the garage, and with all the little rebuild steps ive been doing up til now, I was pretty well committed to starting her today.
Top up oils.  Put a gallon of 50:1 two-stoke mix in the fuel tank (Dan recommended this as a precaution, but I notice that Haynes also suggest this after an engine strip, just to ensure some lubrication while the autolube primes) - connect and adjust rear brake cable, clutch cable....... and then I found myself titting around again with the number plate and the tax disc holder.  Once again I was subconsciously avoiding the big question - would it run?  I snapped out of it and put the ancillaries to one side, and wheeled the scooter out of the garage.  The last time id started it, Id filled my garage and next doors house with white smoke, so I wasnt taking any chances this time.

Ignition on, fuel tap to Aperto, choke out.
Kick one (ooh that new kickstart gear does feel considerably more positive)
Kick two - and she fired into life! But OMG what is that racket?  Whats happened? it sounds worse than it did before the rebuild!  It must have only been seconds but I remember it feeling like an age as the bolt of cold sweat ran down my back and I panicked.  I could see another engine rebuild flash before my eyes as I desperately fumbled to try to work out how to stop the engine - in my panic I seemed to have become blind to the ignition switch.
Turns out that i'd forgotten to put the exhaust pipe and silencer back on!  What an idiot!

So on with the exhaust pipe - and a little reflection - is everything (else) properly in place?
Kick - first time start.  Sweet :-)
But OMG whats that racket?  Bloody hell there is still a clattering in the engine.  Again I felt a wave of depression go over me as I saw a vision of the engine coming out again - can I really be bothered?
It turns out that I could make the clattering stop if I pulled the clutch in - Aha, so maybe its a clutch adjustment thing.  I can fix that later - but first lets see if I can get this thing to drive.
Well yes it does drive, but its not sweet.  its difficult to get it into neutral and it stalls too easily unless you give it considerable revs and clutch slip.
Ok, so it starts and runs, but it looks like im going to be doing some fine tuning and cable adjustments - but it was time for breakfast.

As I sat having my toast and coffee (and this is the cool thing about walking away from a problem and letting your unconscious mind to incubate - I thoroughly recommend it - whenever you have a problem that needs sorting, start by doing nothing!) , it slowly occured to me - I wonder if it would be possible to get the gear-change cables crossed - so that what looks like first gear on the handle bar is actually fourth gear and visaversa - and in that instance, neutral would be at the other end of the twist.
[Vespa has a simple in principle, but potentially complicated and troublesome dual cable arrangement from the handlebar twist to the gear-changer unit on the side of the engine.]

So suitably caffined and warmed up, I went back to the scooter and tried to ride it down our road using the gear-change 'in reverse'
OMG (again) everything is as sweet as a nut!  its perfect!  clutch spot on and gear selection smooth.  And now that I knew where the real neutral was, that awful clattering had disappeared - clearly what id been trying to do was find a neutral INBETWEEN gears - and I think this is exactly what I was hearing in the video I posted a few weeks ago, before the engine rebuild.
Once again - I am a complete idiot - I had literally got my wires crossed!  and was selecting the gears in reverse.  No wonder it wouldnt pull without revs and clutch slip - I was trying to pull away in top gear!

So it was a simple case of swapping the cables over at the gear-selector end (well not quite so simple now that everything was on the engine, but certainly no more than 30 minutes)
Another test run and I am delighted :-)
Everything is as it should be (though I think i need to sort the earth out on those rear indicators)
There is still a fair puff of white smoke.  Im not sure what is acceptable.  Is this smoke from the grease and rebuild oil?  maybe its smoke from the double dose of 2 stroke oil (in the fuel mix and in the auto lube).  I hope its not burning oil from the gearbox now that Ive replace all those oil seals.
ooh and I do need to get those wheels painted!

So now what? there was only so much riding up and down our road I could do - I need to get an MOT, tax and insurance.  Its such a shame that the weather is turning now for the winter - just when I am ready to get out on the road.
Whatever happens now, I do feel relieved and pleased to have got it all to this point - its all been worth it :-)