Measure .... what is the dropout spacing?
if there is cold setting in the plan spread it out to 135..
wider allows the whole hub to move to the right, putting the hub a bit more centered under the rim on the center line.
then get a longer axle.. solid , nut fixed ..as you say ..
i have a huffy mountain bike
so I wouldn't pour much money into the project ..
road bikes were 126 when 6 speed hubs were in vogue. 135 is more like what MTB are now..