Well thanks for all the replies. I guess I should not expect any as I rarely get involved in many threads but you must know that I do appreciate all your input.
I found the owners manual and it says it can lift 2645# at the end of the arms and 1985# 24" inches back from the pin. I have been thinking for the last couple years that if I mess up when lifting logs I could damage the front end.
You see the only time when I will be using the box is when I saw up my firewood. I have a homemade jaw / clamp on the front bucket and I use it for many things. Mainly though for moving tree length hardwood or softwood wood saw logs. With the firewood I lift the entire tree up to a comfortable height and saw into 16" firewood then when I get close to the bucket I drop the log and re-set and lift it again and saw some more. This way I save my back and all my firewood that has to be split falls to the ground in the same place. Then I move In the splitter , split the pile load the trailer and haul it in with my Ranger. But when I lift a tree length Beach or Yellow Birch 50' long,...and 20" on the stump,... that is very heavy on the front end so I do not want to do that anymore without some rear weight.
The bottom of my box is a 2' x 2' galvanized steel plate 5/16 thick. Then I have 3-2.5 inch diameter pieces of galvanized pipe welded at an angle to the plate in the bottom w/ drain holes that are long enough to extend about an inch above the finished box. I will use these to carry a iron rake in one pipe a spade in another and a crow bar in the last pipe.
I have maybe 30# of misc steel in the box welded to different places to provide support and strength to the concrete. I will also be using a real category 1 draw bar as the lower attachment point for the lower arms and I fabbed up some channel iron for a top link connection. The box will extend 12" beyond the lift arm pins. So whatever I said it weighed in the first post it will weigh,..I can probably add 35 to 50 pounds to it I would guess in the steel inside the box. I think I will leave it as is and pour it full in the future. Jeff