Unless you go with the original contraption that Ford used, AFAIK there is no such thing as a booster that'll bolt on without some modification or fabrication.. With a short enough master cylinder(most orig types are too long), the 7" diameter universal units on ebay will fit between firewall and shock tower, at least that is if bolted directly to firewall(adapter brackets are a no no)... It will require drilling firewall, modifing/fabbing the MC lines and hookup of the pedal rod... If a GM MC is not used, you'll probably have to elongate the MC mounting holes slightly... http://www.ebay.com/itm/7-ZINC-POWE...L-A-/300799070248?hash=item4609059028&vxp=mtr BTW if you decide to try one of these from ebay, shop around... Seen them for $35 or less...
If you are converting a manual-brake Maverick/Comet to power brakes, using the stock Mav/Com booster, you will still need to drill some extra holes and replace the brake pedal bracket, etc... as per Craig's Tech Article: http://mmb.maverick.to/resources/converting-to-power-disc-brakes.17/
Maybe, but I had a '67 Falcon Wagon with 289 that had power drums, had reasonably comparable brakes to the '69 Cobra in my sig(both owned at same time)... No doubt would fade on a steep incline long before the discs but I'm on flat land, in a metro area, never found them inadequate... WAIT there was one exception, the time I was towing a yard of concrete... But that weighed nearly as much as the Falcon, wasn't going to be anything even vaguely resembling a quick stop, even if it had discs...
Nothing wrong with drum brakes if you know not to use drums that have been turned too many times and know how to adjust them periodically. Brake shoes have more contact surface than disc pads.