mtd pulley swap

Doing a rear pulley swap on a 600 sires MTD yard machines 16.5hp Briggs OHV, but im not sure how to go about it. ive seen where people have said to grind a flat spot on the trany shaft and just put a set screw, and also to cut out the center of the old pulley and weld it into the new one. i was wondering if anyone has a better way about doing it or if one of these is the best.

any help is appreciated, thanks