I took a lot of pictures, which included a yardstick for dimensions. I will post after midnight when I have reasonable internet speed.
I use a 1-1/8" wretch to snug fine thread bolts. Do not over-muscle bolts, just snug. I keep the 1-1/8" wrench attached to tractor with two rare earth magnets when using the spade. I check tightness of bolts/pads every 3-4 hours. My spade-fit-to-L2296-bucket is absolutely tight and rigid. Fit was equally tight to standard (light) bucket of predecessor Kubota B3300SU but not quite as rigid and B3300SU had less weight and less hydraulic capacity than current
L3560.
Impossible for manufacturers producing a standardized product to allow for aftermarket additions, like your bolt-on edge.
I am surprised you did not immediately think of disruption to fit from aftermarket edge.
Take the aftermarket bucket edge off. I do not know your Vermont conditions but that L2296 is heavy duty in itself.
Until tomorrow, when T-B-N will have my pictures.......which are probably not needed.