Mike,
As you know, there are some folks that are purists and consider it blasphemy to modify any MV beyond its intended use. In respect to the M416, some folks have issue in cutting the rear for a tail gate because the M416 was originally designed to float.
That being said, I think loading my M416 is more difficult without the tail gate and would be much more useful to me, with one ( I don't ever intend to use mine as a boat). I have often toyed with cutting mine.
I think an M416 that dumped would be a great tool for a suburbanite that would like to go get 1/4 ton of mulch to use around the house and such. Not everyone has a use for a deuce dumper.
If building for sale, I would expect to see a well done M416 dump trailer in the range of $1000.
After seeing some of your projects, particularly the Unimog trailer, I am sure that you would make a superb and usefull M416 dump trailer.
Regards,
Rick