In either case, to determine your per-share basis divide your new total basis by the number of shares after the reverse split. You would have to report any capital gains realized on the sale. Even assuming this met the requirements of an exchange, rather than a sale, the exchange of shares of one fund for those of another is a taxable exchange. This is true even if both funds are within the same family of funds. The fund is managed so the share price is constant.
All gain is reported as dividends.
If the share price were constant, you would obviously have neither a gain nor a loss when you sell shares because you are selling the shares for the same price you purchased them. There is no requirement with that form that there be gain or loss on the sale, only a sale or exchange of an investment asset and sales proceeds.