I picked up a 40 inch kidney mower deck for my Gravely today got most of my yard before I run out of energy . I had not used a Gravely with steering brakes , I wasn't real impressed while moving the tractor around with the blade on it . Once I got out mowing I like it.
I'm a little late joining the thread, but....beautiful machine! Maybe your (awesome) friend felt some empathy for you having to deal with that Grillo, and decided to gift you that mint condition Pro-12 - ha! I have never found the steering brakes to be of value when plowing or blowing snow--typically slower speed jobs. But when using mowing decks, particularly of the 50" variety, the steering brake is in indispensable tool.