Thanks to all who provided advice.
I'm still not sure how the deck was bent. I know I have not been backing up and hit something because I very seldom back up while mowing. Also, I don't think I hit a stump or anything similar because I surely would have heard it.
Anyway, I tried to straighten it with my biggest hammer, which is only 3 pounds. Could not tell that I moved the deck at all, so gave up on that idea. I tried to use a wrecking bar as a lever to bend the one side down, but gave up on that because I was afraid I would bend the other side up.
I remembered a shop in Apex, NC that works on dozers, track hoes, etc. Put the mower on the trailer and went to visit the shop. They have a large press but the mower was to big to fit into the press.
They suggested blocking the deck from underneath, putting a thick metal plate on top and hitting it with a BIG sledge hammer. I asked them if they would do it since I don't have a big metal plate or a BIG sledge hammer. Lucky for me they said yes, however, I had to agree that they would not accept any responsibility if something broke.
They took the mower into the shop and put a 6 x 6 on the floor then put the bent part of the mower deck on the 6 x 6. They had a piece of steel about 2 inches thick and a foot square that they put over the spindle hole. One man held a sledge hammer on top of the metal plate while another man hit it with the BIG sledge hammer. After several hits they would check it with a straight edge, move the metal and hit it again. After about a dozen times, the deck was close to being back to the original shape. Holding my straight edge across the spindle hole in all directions shows that it is out of level about a sixteenth of an inch. The guys apologized for not being able to get it perfect - they were afraid if they hit it again it would take it too far the other way. They said if they could have gotten it in the press that they could have made it perfectly flat.
There were 4 guys working on this for about 45 minutes. They used a forklift to get it off the trailer and to keep picking it up so they could reposition the 6 x 6. I had no idea how much this was going to cost but figured the shop labor would be close to $75 to $100 per hour.
When they were done and had it back on the trailer, I walked into the owners office to settle up. He asked me if I thought it was worth $35. After I picked myself up off the floor, I told him I thought was a fair price.
Have not been able to put everything back together yet because it has been raining so much. I'll let you know how well it works.
Bob