How to remove this pump nut?

Another service manager called and asked if I knew how to get this nut off the pump. This engine is in a Link Belt 135 excavator with an Isuzu engine. Anyone have any suggestions?

Build a spanner. Looks to be aluminum so if it isn't galled it probably isn't all that tight. Weld a cheap socket to a piece of plate. Weld something on the plate for teeth. Pieces of roundstock or whatever. 10 minutes and done. Use paint and a piece of cardboard if you want to get dimensions easy. Put paint on the nut and push the cardboard onto the paint.

edit: I forgot to account for the shaft. Weld a piece of pipe to said plate then socket to pipe to go over shaft.

Go to harbor freight and get a socket then cut notches in it to fit that nut.