I think you're supposed to do Sch D on this. If you had only CG distributions from funds, you could get away w/o Sch D but this , I believe, is different. IRS will be comparing the 1099B numbers w/ your Sch D and if you don't report it there, they may wonder why. If you don't have the cost basis records, the official way to do it is, as you suggest to use a basis of 0. How much could you owe on 1 share unless it is BRK-A.
.........and if you're in the 15% bracket, LTCG are taxed at 0% rate anyway so it may be simpler just to use 0 and enjoy the rest of your life.
You should have gotten a brochure describing the merger. Look in the taxation section for more details on what you need to do. Post any questions on the fairmark.com tax forum in the CG subforum. If you
do, the name of the stock might also be useful.
I've usually seen where the fractional part of the converted shares gets turned into cash (but not a whole share......is the rest in round lots of 100, 200,etc.
shares?) For the description, I would put the #shares, stock name or symbol, and perhaps CIL (for cash-in-lieu). Take your best guess at an acquisition date (> 1 yr ago , right?). You'll have to use one of the worksheets.....perhaps QDIV?CG ........to calculate the tax .