[spdbrake]

The Moroso type filler T is already a part of the standpipe, you won't need it and dropping the tanks is not req'd just pulling the r/rear wheel.

The instructions point to either after the collector or on a primary.
I've run a couple of Stangs before with the O2 sensor in one primary (long tube headers) with no ill effects after 135k miles and 3 motors.

To be honest you won't be able to install it above the Horiz plane aft of the collector without punching a good sized hole in the side of the body. The O2 sensor id pretty tall and the the pigtail not so flexible. Would probably end up being just off plumb and being an eyesore. You might try giving Brian (works the Shop and Dyno) a call @ Vintagemotorsports and ask how they mount theirs.