| Actually, I would not worry about lumping the assets together as most large corporations tend to do that, as long as you maintain a detail asset listing. So, there is no reason to amend the prior year 2007 tax return.
Now, that you have sold some of the assets clearly you would have some gain or loss on those assets. I would identify the asset sold and deduct that amount from the lump sum of the assets and separately compute the gain or loss on Form 4797.
I am assuming you are going to consult a CPA or a tax professional to help you to determine the depreciation recapture. Also, do not forget the favorable treatment of losses from sale of business assets, they are treated as ordinary losses. | 
