There was a guy in Top Truck Challenge a few years back with a K5 Blazer running Unimog axles, who had a T-case flipped backwards for overdrive. It seems like he said he had to switch to a different type of bearings because he burned something up the first time he tried it, but after that it worked.
Now that I think about it, he might have been running a 203 range box backwards.
My intial thought is that with a lot of highway usage, especially in a MDT, it would probably have issues.
Are the gears in a 205 straight-cut (spur) gears rather than diagonal (helical gears)? If so, then the direction it spins *might* be less of an issue.