Make sure you have the CT26 side gaskets for the water and oil feeds/drains, and the ones that connect those feeds/drains to the block. One gasket each for the turbo side, one gasket from oil drain to block, and two crush washers from oil feed banjo to block. And yes, it might be an idea to change the CPS O-ring while you're round that side of things.
Oh, and the oil filter - get yourself a Lexus LS400 one - they're a direct fit, and a lot bigger than the stock supra one. Not only that, they're made in Japan instead of the philippines, and much higher quality. I use them on both of mine. Replace it when you take the turbo off, it's so much less of a ballache. If you really want to get down to it - you can remove the oil cooler line to the filter block/takeoff, take that spigot fitting off, and clean it thoroughly, and fit a new spring in there, with new crush washers.