I think both years had control panels but only for the SP models. Check out this 1959 parts manual for model 20119:
http://www.ebay.com/itm/TORO-MOWER-...520?pt=LH_DefaultDomain_0&hash=item1e67566e88
Interestingly, the mower in that manual uses the Tecumseh engine with the gas tank on the back. I know they originally used Briggs & Stratton engines with the fuel tank on the right side. I'd thought this changed for 1960 but perhaps it was a midyear change. Or maybe the SP models always used the Tecumseh? I do know the SP had a bigger engine.
From what I can tell, Toro's early model number system worked like this:
The number starts with 18 for a 19" mower, 19 for a 21" pusher, and 20 for a 21" SP. I can't figure out what the middle numbers mean. The last number indicates the year (9 = 1959 in this case). The 1960 version would be 20110. Also, the serial numbers DO NOT begin with the year of production like newer mowers. It appears they started at number 101.
I've also noticed a couple subtle changes:
- At first, there were stripes on the shroud above the bull head and later it changed to a single block, probably when they redesigned it for the Tecumseh.
- The newer ones have a 19/21 Whirlwind sticker on the deck in front of the engine, the old ones do not.
One other thing, I'm pretty sure that neither the bagger setup nor the deflector can interchange with later mowers.
EDIT: I take back the comment about the sticker, I finally noticed that the earliest models had it. Here are the two earliest ads I've seen, from May and September 1959. Perhaps someone with better computer skills can upload them to this thread. One subtle difference in these ads: the early ad has the usual zigzag tires while the second ad has "grooved" tires.
http://books.google.com/books?id=YE...AEwAA#v=onepage&q=1959 toro whirlwind&f=false
http://books.google.com/books?id=u0...AEwAQ#v=onepage&q=1959 toro whirlwind&f=false