classic motorcycle forum

We do need younger people to get involved otherwise all our old bikes will end up as landfill, museum pieces or decorations in trendy coffee bars.

The world (and young peoples' interests) have moved on, and that's why things like aero-modelling, live steam modelling, old bikes and cars etc are only for the white-haired people.
People (young or old) either "get" the passion for oily dirty things or they don't, and since the advent of cars and bikes that don't need regular fettling/repairing/rebuilding sessions the opportunity to personally learn of get involved is limited.
The VMCC (for example) is always whittering on about the need to get the young involved but to me, it's thankless hopeless task. When I'm gone my bikes will be sold, and if they achieve £thousands or ten bob a ton won't make any difference to me...I'll have had my enjoyment out of them.

Oil drops out of the breather is usually the result of poor crankcase scavenging. Triumph plunger pumps aren't known for unreliability, so a sensible step would be the good old "rubber pipe on the oil pick-up pipe and finger over the oil port" trick to see if the pickup pipe has either cracked or started to leak at it's crankcase entry point.

A Siemens relay could be used on a multitude of different equipment. What are it's functions?

If it was relatively easy to up a 650 to a 750 then the old Morgo kits wouldn't have sold as many as they did. Don't know why they were so popular anyway as the 650 was a nicer engine than the 750.

Reason I said about the stampings was because I was wondering whether you had a T120 with a T140 engine over-stamped.
Excessively skimmed drum or worn out shoes?  Go for the obvious first...worn shoes.

As a Scott owner and forum member I've seen similar scenarios to yours several times now. 
"I've just bought/rebuilt this old Scott and it won't run for more than a couple of pops, please help" is the typical question.
The old hands always answer that on a primitive two-stroke oil is an essential part of the sealing (compression) process, and if the seals, rings etc are dry then sealing is poor to non-existent and it ain't gonna run.
The Scott has removable covers over the transfer ports and the standard reply is to take these off and give the workings a good dose of thick oil. I know yours won't have these removable covers but it's something to consider. After all, when Pierre used to ride that bike daily to the garlic factory the engine never dried out, and no-one would buy a bike for the daily grind which couldn't be started.

Have you tried starting rollers?

The British old bike enthusiasts are notoriously as tight as a duck's drum.
I was at Netley Marsh last Friday, and heard that immortal exchange-

"How much is this mate?"
" I dunno...give me a quid"
"Nah, far too much..make it 50p and I'll take it".

So there's this way of thinking amongst all the normal old riders, and those who spring £50K for a Vin or whatever, and your bike falls smack in the middle.Too dear for some, no marketable quality for others. Have you tried the Jap home market?