I am a SALT person so def not the most qualified to answer this, but I can point out a few flaws I see.

First of all you are recognizing a gain of the boot received and this needs to be taken into consideration when computing your basis in the stock received.  Otherwise you would effectivly be taxing yourself both on the boot received as well as the gain when you sell the asset with a basis that is too small.  I would expect it to be something like this:

40,000,000(basis in prop given up) + 30,000,000(boot received) - 30,000,000(gain recognized) = 40,000,000 basis in stock

While this ends up basically being a carryover basis this is not always the case as you take the lesser of value of boot received or gain realized.

The holding period depends on if you are transfering section 1231/capital assets.  If you are than the holding period is typically the holding period of the transfered asset.  If not than it begins at the date of transfer.  This would be true for the boot as well as the stock.