Well the 580 came with a Briggs so see if the clutch drive plate will fit the Vanguard from a 16hp opposed Briggs. You can make an adaptor plate from the clutch drive plate to a hydro drive shaft.

On the pto???? you may have to find a 1" pto for a Vanguard, just check pulley size for a match, 4" X 5/8" ???? I think???

Or any one with a 1" id bearing and then adapt it to the bolt pattern on the mounting plate to the Vanguard.

Scott