I am going to use the county tax assessment percentage to calculate the land value.
in some cases, this is not a valid method. some counties value land at x% of FMV while the building is valued a y% of FMV. check with your county's assessor's office. then you'll know how to use assessed value to allocate cost. (example land valued at 10% assessed value $10K thus FMV = $100K building assessed at 15% assessed value $75K thus FMV $500K . thus of your cost basis, 500/600 allocated to the building.
you would use the current year's values. what you cite is based on the property purchased being used immediately as a rental property. that's not your situation. for a better example read page 15 of PUB 527.
