I will start by saying I like the idea of running light, as I run an oddball setup too..
The one issue I possibly see with your idea is you are kind of putting all your eggs in one basket.. If your direct shipper is slow, or goes under he could take you out with him.. As you probably know, the open deck segment is hitting a bit of a slump right now, at least for some of us.. This might not be the best time to jump in, but if you think your guy can keep you busy, at least fuel is cheap..
A 42' highboy with a limited weight capacity (single axle t600 of yours) will be a killer for load board freight. I'd personally try & find a step. Lots more to pick from in the feather weight division if you can take ~126"-128" tall, 48' long, & ramp load/unload stuff.. Pulling a 48' I'm guessing is not much more difficult than a 42', unless you have to get into really small delivery sites..
That's all I have, & wish you luck. Love to see another single screw out here pulling open deck..!