Here are some issues to watch out for:

1. The value of TruePosition is uncertain.  I assumed $300M.  See my post on TruePosition and on the Broadband spin.
2. The present value of the deferred tax liabilities is uncertain.  It might be reasonable to assume that $1 due in the future is worth $0.20 today.  I think that Malone will not dispose of his Charter or TWC shares in a tax-inefficient manner any time soon.  He could conceivably hold onto Charter for decades.  He may very well swap TWC shares with TWC for shares in the TWC+Comcast spinoff that will be managed by Charter.  So, I think that he will defer the taxes on TWC shares for a very, very long time.
3. I have no idea what the cost basis is for the TWC shares.  I suspect that it is something extremely low.  However, Broadband’s financial statements in the S-1 spinoff filing shows that Broadband’s deferred tax liabilities are extremely low.  In any case, the DTLs on the TWC shares aren’t particularly significant.
4. EDIT (8/26/2014): I don’t think I handled the call options that were sold on the TWC shares correctly.
5. I ignore all of Liberty Broadband’s other assets and liabilities.  I don’t think that they are material compared to what TruePosition is worth.
6. I may have performed the rights offering calculation incorrectly.
7. I may have handled the diluted share count incorrectly.

*Disclosure:  I already own LMCA.  My plan is to hold onto my shares of the parent and the spinoff.