I just recently got a Hi/lo for a simplicity small frame. How much you may ask? FREE!!!
Our cousin ryan gave it to us. said he paid 2 bucks for it. Sweet!
Imma put 'er ont the 637 yeoman for leaf blowing and for snow blowing.
As for the rototiller, probly not. see the thing with the hi/lo's are that they reduce the rear PTO spped to by the same ammount that it reduces your speed.