First partial tank result is in. I had burned 1/4 of a tank before doing these mods, and this morning, with 744km (462mi) since my last fill up, I put 38.3L (10.1USgal) into the tank, for a record fuel economy of 5.15L/100km (45.6mi/USgal, 54.8mi/ImpGal).
I'm hoping for even better next fill-up, where the whole tank will be with the mods in place. After that, I'm going to put on smooth wheel covers.