I would guess 500 pounds at the most. I bought a 3240 2 bottom at an auction and rather than wait for the loader three of us lifted it up into the back of my truck. It was all we wanted to do it, so I'm guessing it is around 300 (100 pounds per person to lift it.) Add another bottom on will probably be about another 150, so 450-500 pounds sounds good. As long as it isn't a lawn and garden cart, I think you should be fine.

The 3240 was made starting in the mid 1950s, targeted to go with the Super 55. By 1960, possibly earlier they were upgraded to the 3241. So I would say they were made for about 5 years. Maybe someone else can add to that.