Ok, I’m not sure exactly where in the drawing you are planning on putting bumpers. Having said that I believe you could make a legal configuration out of this frame provided the two front flat surfaces are 6" long each.
Assuming the robot is 28X38 your bumper perimeter is 132" and yoiu need to cover 88" with bumpers.
It appears that there would be no reason not to cover both long sides with this design giving you 76". To properly cover the corners you would then need 2 6" segments on each of the short sides for a total of 24" which brings you well over the required 88".
If the angled pieces on the front are supposed to be bumpers these are not “official” bumpers and would count for robot weight and volume (and this cannot extend outside the bumper perimeter and would be illegal in the configuration shown. Removing these bumpers (and enough in the back to make a space for the trailer hitch would result in a legal configuration.