Walk Behind Lawn Mowers

I have a HU700F with the serial # worn off. I need a gearcase assy complete and ordered (532404834 & 589600601) and they are both wrong. The drive shaft ,on the wrong ones, are both 21 inches long and the one I want to replace is only 19 inches. From your site I get the numbers (5324246-57 & 5324091-48). I am at a loss as to what # to order. I would appreciate your help in this matter.
Thanks
P.S. My e-mail is rexshupe@hotmail.com