I grew up mowing with a gravely. I guess I started mowing with my dads old gravely when I was about 10 (1965). When I was about 12 my brother took it with the saw blade attachment and was helping the neighbor clean his fence row. He left it in their barn and the barn burned down that night.
We ended up with a brand new gravely and my dad was very proud of it. I mowed with it until I left home at 18 and trust me, if I couldn't tear it up, it was a tough machine. We mowed in the summer with it and in the winter put duals and weights on it and plowed snow. I remember after a big snow I had my buddy lay on the hood for extra weight while I plowed the driveway.
I now have a ZTR Gravely, but it isn't the same.
As far as engaging the mower, if I remember correctly, we put the hi-lo in neutral and as you pulled the mower lever, slightly bumped reverse.