Hey Lakeracer , From some research I've done { DO NOT TAKE IT TO THE BANK AS I HAVE NOT CONFIRMED THIS} it seems the starters on the 18hp , 20hp,and 25hp from 1957' to 1977' are typical that is interchangable , however the bracket is not, I 'm not sure of the starter bendix. It would seem logical in your case that the 57' and 58' models used a similar cowl that you would need a 57' or 58' bracket because the 59' and early 60' model used a completely different design 1 piece cowl, they probably deleted the cowl mounts on the bracket as unneeded. If you find out anymore info post it here, I'll do the same, and hopefully soon we'll both be able to push a button instead of pulling a rope.