The frame looks like a Yamaha YG1 (early 80cc,rotary valve).
Heres a pic of a YG1.
I think I have a service manual for that
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1963-71 rotary valve singles
Suzuki T20 is 200cc twin.
The tank is a Yamaha one as Suzuki (usually) used a round badge with just the stylised 'S'
It's probably been impossible to get left silencer for years which is why it just has straight pipe.
Never seen a trail version before but I know a man who may have.
I'll e-mail him and get back to you
PJ