"Do I just pay taxes on the cash or boot received?"
No. This was a fully taxable transaction. You deduct your basis from the entire proceeds (cash + stock) and report a gain or loss accordingly.
"Does my original basis in Rockwell Collins become my basis in UTX stock?"
No. You have a new basis that's the same, on a per share basis, as the value used for the "stock" portion of the proceeds.
"Do I manipulate the basis on the form 8949 so my gain equals the cash I received?"
No.
Tom Young
NOTE TO FUTURE READERS OF THIS ANSWER:
You must understand that the answer given is relevant to this particular transaction. There simply is no one or two sentence answer that covers all cash + stock mergers/acquisitions.
