They say two routes go north to Wiang Haeng.
The mountain way and the river way.
Thinking the road you describe ain't it.
The river way is well signed at the NE corner of town.
Mountain way prolly no stream crossing.
Guessing.
Have him deliver to Land Transport Office
and hire an agent there.
Agents set up shop there.
Otherwise no-go.
You will need a certificate of residency from Immigration.
That's it.
Prolly all decent bikes.
None going to be overly comfortable.
Twin would be cool.
& able to attach rear rack.?
Are you buying from dealer
or looking online.?