This would not be the conveyance of an undivided interest. This would require a survey to describe by metes and bounds the specific portion of the 4.3 acres that is being conveyed by deed to the buyer. That solves the tax problem too. The conveyance of an "undivided" interest is the transfer of a fraction of every grain of dirt, not the transfer of a specific part of the entire tract. You also need to think about whether or not the portion your retain will have ingress and egress and whether or not it will be marketable. If not you may want to require a buyer to purchase the entire tract but you adjust the price per acre. You also need to consider the mineral rights.
DISCLAIMER: This is not specific legal advice and does not establish an attorney/client relationship.