I don't think selling would have made it any less of a mess. If you had sold before the merger, I think you would have had these same issues. The merger for tax purposes is basically a forced "sale."
I think I'm slowly figuring it out.
Here's one that helps:
https://www.bogleheads.org/forum/viewtopic.php?f=2&t=159254&newpost=2391567
This one, too. Seems a little simpler:
https://ttlc.intuit.com/questions/2737490-how-do-i-account-for-sale-of-kmp-turbotax-for-2014-return-holders-were-forced-to-sell-their-interest-in-kmp-so-how-to-account-for-sale-of-an-mlp-in-turbotax
How to report the sale of a MLP such as KMP where the sale is reported on a 1099-B.
To force your ordinary gain portion of the sale onto a 8949 form:
1. Go go business items and open the K1.
2. Follow directions to report that you sold your partnership interest
3. Enter a sale price of 0 and a partnership basis of zero.
4. do enter the ordinary gains from your IRC 751 statement in ordinary gains
5. adjust the amount for AMT and enter that in the right column.
To force the capital gain section onto an 8949 form:
1. Open the 1099-B
2. You need to adjust the cost basis in either box B (short term) or Box E (long term) or both depending upon when shares were acquired.
3. Calculate your basis this way:
Original cost + adjustments to tax basis + Ordinary gains (entered on the k1)