Hi Barry, having a look at the Parts List for the Diplomat, the engine shaft is secured to the output shaft of the Briggs with a 6mm grub screw....we need a pic of the inner cutter clutch half to see how that is secured; as grumpy said with a captive cotter pin or grub screws. Looking forward to seeing the pics!
Please do not PM me asking for support. Please post your questions in the appropriate forums, as the replies it may receive may help all members, not just the individual member. Kindest Regards, Darryl