Can you purchase just the 520 frame and fork from Trek and may I ask your cost if you don't me poking my nose in here?
Btw, your 38x11 at 90 rpm's is maxed out at 25 mph which may or may not be fast enough for you. I would want at least a 42 big ring up front and that can easily be done with a mountain bike crank, of which you can remove a chainring if you want to maintain a double up front.
Best of luck with your build.