The 260 is certainly worthy of a full restoration, but at the end of the day, the decision also depends on what you plan to do with the car. If your goal is to restore and flip the car for profit, neither may be a good option. Cost of a restoration typically is more than immediate market value. The 240Z is considered more desirable by collectors, especially the earlier years. Given you won't have the correct size engine & transmission, it will be considered a resto-mod and worth a bit less than an "original" car. The 260Z will still be marketable, but perhaps to a somewhat smaller number of buyers. If you plan to keep the car, they are pretty much equal in terms of value for your investment. Just my 2 cents...