I ended up finding that too after I did my own spreadsheet and calculated and recorded every darn single entry. Matter of fact I was going to post it but you already did 🙂 It saved me $25 or so but the detail oriented person that I am is glad that I have it all documented moving forward. I ended up using the instructions below in my 1099. So basically it's the "conversion factor" times the cost of the account up to that point for each and every measly transaction.
"This transaction represents the sale of assets from a Widely Held Fixed Investment Trust (WHFIT). The cost basis allocation factor is the value of the assets sold divided by the total net asset
value of the trust. If you know your cost of the assets sold, use that to determine your gain/loss. Otherwise, determine your cost basis by multiplying your adjusted cost basis by the cost basis
allocation factor. For example, if your adjusted basis is $1,000 and the cost basis allocation factor is 0.005 your cost basis allocated to that sale is $1,000 * 0.005 or $5. If there are subsequent
sales of trust assets, your adjusted cost basis for the next sale is $995. Sales are reported based on when and for how much the trust sold the asset. This may differ both in timing and amount
from what is distributed. There are cases where the proceeds are used to pay expenses and there is no corresponding distribution. For more information refer to regulations section 1.671-5."
