Okay so I got the car, and got a chance to see the underbody while it was on a lift. No pictures, sorry
I'll try to include some at some point.
The middle section of the chassis is around 1-2 inches higher than where the rest of the plastic underbody bits sit. Not good, it will take very large amounts of coroplast to fix :/
I may consider buying a full sized mid section brace and using that as a frame to hold a huge coroplast piece on, but they're kind of expensive and the car already has an aluminum "breastplate".
I misspoke about the front radiator vent. Looking at it closely, Toyota made the underbody vent quite aerodynamic. It has slits cut into the plastic blocking off half the area though, which I think I'll cut to free up some flow, while blocking the unruly flow that makes it away from that vent.
The car has a front underbody brace, which can be an attachment point for a sheet of plastic, if I am willing to use zip ties to do it. It's under the car so I guess no one will ever see it...
The rear is missing all the splash shields, which is a little annoying. I am trying to buy a stock splash shield for the engine and transmission, but will cut access holes for the oil drain plug and filter so it doesn't have to come off every single time. The stock engine splash shield is pretty smooth.
I recall 2-3 years ago studying the rear and concluding that an aluminum diffuser would be very easy to make, thus it's in the plans. I was originally getting kind of ambitious and thinking I wanted to bend aluminum sheet to make the strakes that block off the vortices from the rear wheels, but that's probably a bad idea, I'll go with plastic or rubber for easy cutting.
Front grille has TRD foglamps which block off some of the grille, but not efficiently. The mesh pattern plastic protecting the radiator was cut up for the foglamps unfortunately, and the radiator fins are pretty bent from eating 210k miles worth of rocks. I am considering taking the plastic mesh out completely, allowing for a perfectly smooth radiator duct that should be quite efficient. Since the opening is going to be much smaller, I imagine large objects going into the radiator won't be a huge concern...I hope?
Car is dropped I think 1.7" right now. It's a little low for psychological comfort, even though I haven't scraped it yet. Better to raise it a bit though, which will give up some aero due to more tire being exposed.
The rear deck is a little too low to hit the template, and I'm still debating whether I should get the Luxurypart spoiler or the Duraflex Type W spoiler. The Duraflex is really big, but apparently doesn't have good fitment.
VIS dropped the price on its hardtops again, so now I'm getting tempted. I think if I put dark window film onto the rear glass that it might not look so bad...
Racing mirrors are a lot of effort to mount to the car...maybe I can 3d print one?