Rick, I agree with the locking handle impacting the way the machine runs. An OP just isn't meant to run that way. The orbot and others have resolved this by attaching the handle to the wheel chassis and allowing the head to float and pivot. Unfortunately that would be quite a bit of modifying in the case of the lowboy or challenger. Kinda like trying to make an old dog do a new trick. IMHO a simple add on wheel kit that the average guy could install with solution tank for the lowboy would more than suffice and make that machine a very cost effective alternative for mid sized commercial jobs.
I'm sure you'll come up with something nice!
I'm sure you'll come up with something nice!