They used to post on TRDforums several years ago. One had a white 7th gen wagon, used the side skirts from the TRD package (curiously, they were a bolt on affair, as same wheelbase between the 7th gen and 8th gen). Fair amount of body work on the front, as the 8th gen bumper and hood lines up differently compared to the 7th gen. Rear, just kept the OEM 7th gen. Think he mentioned that it was more involved than just the bumper cover - radiator support need to be modded, brackets removed/moved, front reinforced bar need to be dropped, etc.
Some of them kept the 7th gen projector style lamps and modded the bumper to fit, the white wagon kept the 2001 style lamps. Think that owner was from P.R. - big Toyota community there. Really no good DIY guides out there, as this is too custom of a job to write something up - varying levels of fabrication experience made for different approaches to the swap. Those with metal fabrication/cutting/welding experience added new bracket where needed, those with more fiberglass/molding experience modded the bumper cover to "fit" the existing points, bolted on sheet metal brackets where strength was needed.