This has always been my pet peeve with hotrod aftermarket parts suppliers. They rarely include a set of instructions for their materials. Using the "assume" logic whereby their assumption that you know exactly what you're doing makes an "*** " of "u" and "me" (assume).
Model A frames in the aftermarket (TCI, Chassis Engineering, etc.) are so cheap I wonder why anyone would bother boxing an original 70-odd year old frame.
That said, virtually all add-ons to hotrod frames are made and designed to mount to a box-section frame usually with weld-on bracketry, sometimes with through-bolts (when using thru-bolts always weld a tube into the mounting hole to eliminate compression of the rail.
The placement of your pedal/mastercyl/booster assembly is dictated by the clearances you have on that side and your personal ergonomics for pedal placement. Always make sure the pedal is easily accessible! Believe me, I've seen many pedals behind steering columns and not sticking through the floor enough for full travel.
Remember, this is your car and should be built to your leg length, your body structure, your arm reach, your headroom!
Check through old issues of street rod magazines and you'll probably find an article showing a completed chassis which will illustrate one way on mounting your brake controls.
Your car's most important functions to keep you and yours alive is that it STEERS and STOPS SAFELY.
Enjoy the street!