Sam, I must say I did not completely follow the original post or the comments, as this is very much an "off the post situation". I bought a block of land, and the same day I signed, I then entered into a contract to sell half the land, with settlement due when the subdivision, and title arived. I had letter from 3 agents, giving a value, as at the date of the contract, and that covered ATO, and the local State Revenue Office. So my thoughts are, look at the wording of your agreement, at the date of entering into it, and the conditions, in particular when, the change eventuates. If all worded correctly, it may work for you. Please keep us informed.