Yep, as expected this is not simple.
First, you need to figure the adjusted cost basis of your original 66-67% after having dealt with the final K-1.
Take the original cost basis of that 67%, add to it the cost basis (or share thereof) any property improvements you paid for during the period of time it was in the LLC. From that total, subtract the total amount of depreciation taken on all assets (That is to say, your share of depreciation on all assets). This will give you the adjusted cost basis of your original 67%.
Add to that adjusted cost basis whatever amount you paid the partner for their 33%, and that total gives you your new cost basis that will be used on the SCH E part 1.
So assuming no property improvements were done in 2021 after the LLC was dissolved, you'll only have one single entry in the assets/depreciation section for your "new" acquisition. Depreciation will start all over using the new cost basis, for the next 27.5 years.
For mortgage interest, you will need to see what was claimed (by both you and your partner) on the LLC 1065 return, The remainder will be claimed on the SCH E by you. Same holds true for property taxes and insurance.
The math may take a bit, as you'll have to look at the ALTA closing statement you received when you closed on the purchase of your partner's share to see if you paid your partner or were reimbursed by the partner for a portion of property taxes they paid, and possibly for any portion of the insurance they paid. You'll want to be careful that you don't "double dip" on those or any other items without realizing it.
Now, for figuring which part of your newly figured cost basis to apply to the land, what you do is pull out your latest property tax bill for that property. Take a look at the tax values and you want to figure what percentage of the total tax value is allocated to the land. Use that percentage to determine what percentage of your cost basis to allocate to the land. (This is the preferred method of the IRS.)
