I have an older Jacobsen Commercial Walk-Behind 12.5hp Kawasaki with a 50" mower deck. The mower is Model 68491 Serial 1638. Problem is no parts are made for this anymore and I need to replace the blades, however cannot find any specs on what size they are. In the parts list for this mower they are listed as Part #390481 Bar, Cutter Any information on the size of these blades would be great! Thanks for your help.