Progress so far...

Ok so I didn't have a scale to measure such small quantities to weigh the floats, but a bench test of the carbs seemed ok re the float and float valve operation. So now armed with some "Cellulose thinners" or "Laquer thinners", depending on your geographical location. I pulled the carbs off again and rebuilt the number 5/6 carb. Now I know what a proper flow of fuel through the idle jet looks like! Not just trickling or even pouring out as it was before, but a vertical pointed powerful blast...Ah now that is an improvement!  . So powerful that I got it full in the eye as it bounced off my cheek and under my safety glasses!  . Maybe it makes a good eye wash? I don't recommend it though.

I could/should have decided to do the other carbs at that point, but being the proud owner of some pod filters it takes a few short minutes to put the carbs on.

Great result! cylinders 5 and 6 are now running and the bike is even idling ...very happy!  But I was still getting some popping and farting from the other 2 carbs. but the 5/6 carb was as smooth as silk.  So off they came for a rebuild on the other 2 carbs. 

So with a 5 hour group ride set for the following morning to the Mediterranean sea, I managed to get the carbs cleaned and back on the night before. I felt optimistic and thought that would be a proper test run for the bike.

Sure enough the bike idled well with no popping or farting from any carbs. So on that front a success! I didn't do anything other than change cleaning fluid. The Cellulose/Lacquer thinners really is the magic ingredient. I'll never bother with "carb cleaners" again.

The ride was a good test for the cylinders and it's oil drinking issue. Plus the less the perfect honing...  I was happy to see that it was still full of oil when I got back.  Normally I'd be putting at least a liter and a half back in after a ride like that. It didn't smoke at all. Success there too! I'll have to look at the plugs later.

The only issue I did have was the temperature gauge hit the red when going slowly through traffic.  I had to stop and let it cool for a while. The weather was super hot, probably 45 degrees I think.    The temperature of the bike is fine when moving...the faster the better. but the fan can't seem to cope. I have a manual switched fan which I always switch on immediately when going slowly or stationary. And I keep a very close eye on the temperature gauge.
Maybe a 7 blade fan would be a good idea? as I'm not sure what else I can do to keep it cooler....Still, very happy with how this is running now.

I'm glad to hear that your perserverence has paid-off !
"Now I know what a proper flow of fuel through the idle jet looks like! Not just trickling or even pouring out as it was before, but a vertical pointed powerful blast...Ah now that is an improvement!"
I found this interesting. I take for granted what the "Streams" should look like. Your comment in this regard is noteworthy for others, using the Cleaning Tool.
Great result! cylinders 5 and 6 are now running and the bike is even idling ...very happy! But I was still getting some popping and farting from the other 2 carbs. but the 5/6 carb was as smooth as silk. So off they came for a rebuild on the other 2 carbs.
And as a result your 5 hour ride was a success, as well !
The Cellulose/Lacquer thinners really is the magic ingredient. I'll never bother with "carb cleaners" again.
This is the only cleaner/solvent I use in the shop.....for damned near everything ! It is "Magic" !   Note however, that this fluid will disolve some plastics and remove most paints. Orings and seals in carburettors are OK because of the limited exposure ( when using the Cleaning tool )
The only issue I did have was the temperature gauge hit the red when going slowly through trafficMaybe a 7 blade fan would be a good idea? as I'm not sure what else I can do to keep it cooler....
There's been previous disccussions regarding "fan improvements". Forego trying to modify an alternative fan. I believe the OEM fan blade is as efficient as you can get.I'll suggest you re-burp the radiator. Even a small amount of air in the system will have a noteable detrement to the cooling. You made no comment regarding a "manual fan-switch". If you don't have one installed - do it !
Carry on ! .....and Kudos !

An additional comment:  The carb.-sync. should be checked every time the carbs are re-installed !!!!!!

Thanks Scotch!    It's true, knowing what the stream of fluid from a carb jet should look like, is a case of seeing is believing...or  at least understanding. I really thought I'd nailed it first "times" around. 
 Another great thing is the Lacquer thinners is a lot cheaper than commercial carb cleaner too, a win win situation.

To be honest your carb cleaning tool was also the magic ingredient. To push the thinners through the carb... in reverse direction... at high pressure... I can't see how I would have unblocked them any other way... I've got to hand it to you, your cleaning tool is a work of genius!

Ok thanks, I'm happy not to buy another fan,   I'll try and re burp the cooling system and go from there.  I do like the manual fan switch as I can preempt overheating situations, such as pulling up at red lights etc. I'm one of those slightly obsessed "check your gauges constantly" kind of person.

Good point, carb sync is on my "to do" list, along with trying out my colortune, ...now I actually have a proper flow of fuel at idle.