Maybe I was/am thinking too hard about this. My original doubt was about how to adjust the cost basis and its corresponding relationship to the cash received. The tax impact worksheet only presented a single example, where the person has low cost basis in FNFG, one less than ($11.70 * 0.68)/share so that after the stock exchange their new KEY shares have a total value greater than the original FNFG purchase. In that case the total "realized gain" is larger than the cash received, so it is logical for the person to only be responsible for paying taxes on the actual cash received, leaving the remainder of this "realized gain" as unrealized, to be captured as a future capital gain whenever the KEY shares are sold. Meaning that the original FNFG cost basis would remain in place undisturbed by the merger.
In the example given in our thread here, the new KEY stock allotment has a lower basis than the original FNFG creating a capital loss, though a loss which is less that the cash payout. This situation was not highlighted completely in the tax impact worksheet. It would have been more clear (to me at least) if the worksheet had described this more like if your new basis < old basis then subtract that capital loss from your cash payout to determine your taxable income. A case where the merger is creating both a small capital loss and positive income at the same time.
....Meaning I agree with the analysis of a $6.40 gain and a $198.90 new basis for Mustachian @rugorak. (Ignoring effects of brokerage fees in all of this discussion).
A third situation occurs if one originally paid more than ("11.70 * .68) + 2.30" or $10.256 per share. In which case the "realized gain" would be negative. So no taxes on the cash payout, but seems like one would be able to adjust their new KEY basis above $11.70/share to reflect that some of their capital loss has not been realized yet. This case was not highlighted at all.