Unfortunately storage space is always at a premium around here for everything and making it longer means I can't get 6 wagons into a storage building. 2 rows 3 deep side by side. Can just get doors shut now and lengthening out the front or back will mess that plan up.

Under the front slope would be ideal. I might see how much work it would be to separate box from gear and lift into place from the bottom on brackets. If that is too cramped or not easily feasible I think I will do 2 channels under and across both stringers to help support the frame off the side. I've got a good supply of 1/4" thick by like 4" channel from a tear down project that would work pretty well for this.

This will not really extend things beyond the width of the top of the gravity box much if at all so overall width will remain nearly the same plus it will also mean it can be removable for use in other applications should the need arise.

Thanks to everyone for suggestions and ideas.