The SU may not help much. oddly, engines at different as the Series changed or was upgraded.Howdy peacockck, welcome to the tractor forum.
Attached below is a Shibaura SU1540 listed in salvage. Couldn't find an SP1540
Looks as if the SP1500, SP1540 and SP1540LP all use the same primary engine block. Bet all the other engines in the parts manual for the other machines would mate up to your machine too. Look at the options.Does anyone know of or have a Shibaura SP1540 they're not using. I'm chasing one for parts. Cheers.