The search for sprockets has succeeded! Rear sprockets for Yamaha TX/XS 650 twins use 530 chain and bolt right on to TR-1 hub. Spacer had to be machined to substitute for thickness of chain enclosure. Front sprocket for Yamaha 650 or Honda Superhawk (CB77) fits on transmission output shaft, but TR-1 sprocket retainer ring will not fit because bolt holes in TR-1 sprocket are further apart. Honda sprocket retainer ring will work, but may be hard to find. Results: higher gearing (18/34 instead of 16/35), reduced unsprung weight, modern 530 o-ring chain.    

Sounds interesting! How much does the engine rev at 100 kph??
Is it possible to use the caincover anyway (I think the increased unsprung weight is worth the price of not having to hassle with a dirty chain!) My bike is a 1981 Tr1 (with the original chain still good after more than 60000 km).

I haven't got it back together yet as I am waiting for new swing arm bearing seals and it's winter.  I will post new speeds in gears when the bike is on the road. I don't think the 530 chain will work with the enclosure because both sprockets are smaller and the chain will likely interfere with the enclosure and rubber covers.  Regearing with standard 630 chain was impossible because no sprockets were available in non-standard sizes.