Man these are all to tough, but for a driver of His Siskiyou I will go with Buddy Thomas.
For what little it is no doubt worth here is how I come up with a guess of Buddy Thomas.
I looked His Siskiyou up in the 1947 USTA year book. It showed he raced only once as a two year old in 1947.
That was on Aug 13 at Butler PA. in the class 18 trot for a purse of $400. He didn't get a check and it didn't show a driver, but Buddy Thomas won the class 23 trot in three straight heats with Josedale Counsel. So I guessed that good old Buddy had more then one trotter at Butler.