i am pretty sure some welding (or securing some other way) would be needed to prevent the rollers from twisting and flopping around
notice the weld in the center of the unit
Go to west marine and purchase a pair of rollers that match the ones you have currently, with axles. Then go to Home D and buy a piece of aluminum flate stock, make some measurements, cut it and drill for both rollers, let the hinge point be the existing bracket. Use a couple 1/2" bolts on each side to put it all together and profit?
I like the rollers that were added to Macs trailer, makes it way easier.