I'm getting closer! Built the rear wheel up, triple-checked to make sure both wheels fit in the frame. I compared it to my Cervelo, and It looks like the sizing is almost identical. The 17.5" Trek is apparently equivalent to a 54cm road frame, at least as far as virtual TT goes.
This build will have a fairly high bottom bracket, so that should be interesting. I measured the toe-overlap with the front wheel, and I should have ample clearance. I put on the stem, handlebar and brake levers just to see how that would come together, and it looks pretty good. I'll have to get some spacers under the stem, and maybe swap it for something shorter - ~90mm should do it.