the 19.5s on my trailer are 0ET, or close to it. Smike's are probably 24-30mm ET. It would be a frame to tire clearance issue. I think Smike's will fit fine on the wedge if and only if the one remaining inner splash shield is removed. I don't think they'll clear on the lowboy.
(dunno what ET stands for, but offset of mounting surface from wheel centerline)
will that coupler go onto a square tube? says it is for round tube..
where does it say that? that one has no tube at all. I see no confirmation on being able to attach to square vs round anywhere though. nor could I find a site for T.E.M., the manufacturer.
I only see that coupler listed with square tube in the full assembly with the fancy height adjuster thing.