I think you are on the high side. I come up with about 40mil in salary leaving us with about 20. I listed the following from most likely salary to least likely.

1. Parker, Duncan, Green, DeColo (Guar) = 28mil
2. Leonard (TO) = 1.9mil
3. Diaw, Mills (PO) = 5.8mil - I don't see either outplaying that contract.
4. Rookie Draft spot = 1mil [tops] - could be traded but if they are letting several guys go, seems like they would keep this pick
5. Splitter (QO) = 4.9mil - No way we don't offer this to him and unless he tanks this year or shows signs of never improving, I think he stays. The only way he gets dropped is if we get a guarantee from a FA and need to shed an extra 5mil. So at this point I count his salary.
6. Joseph (TO) = 1.1mil - Seems too early for the team to pass on him considering his potential to improve and the small contract with options the next 3 years.
7. Neal(QO) = 1.1mil - This number is low enough that I think we hang on unless we are just shedding cash. His shooting and experience are helpful and reasonable for that salary.

All of these add up to 44mil.
The first 4 add up to 37mil, but leaves us with only 8 guys, so technically another 4mil would be added to 'fill the roster'. (this is why we might as well keep Jo and Neal, since they don't cost that much more than a min sal player)

No matter what we are falling in the 40-45 million range, so assuming a 60mil cap, that only leaves us 15-20 to play with. Smith could be looking at the 16-18 range. So it could be tight to get both.

Always the option of a sign and trade to move a little of our guaranteed money with Green, De Colo, and draft pick. This is part of the reason why Duncan's 10mil (compared to an 8mil) hurts. It is also why Diaws deal is such a pain. That extra couple mil could have really altered things.

This is why I also wonder if we don't wait until '14, re-sign gino and just wait out the contracts.