At the time I put that article on my website (~5 years ago), I didn't have a factory '68 brake booster to use (my '68 came with manual 4-wheel drum brakes).
However, I did have a totalled out '90 5.0L Mustang GT that I robbed the fuel injected 5.0L engine, T-5, computer and wiring harness from. The wrecked '90 GT also had the 5.0L brake booster in it, so I decided to try and adapt it to my '68, since it was there for the using.
I'm fairly certain that the booster would work in the '69/'70 body as well, since the engine compartment of the '67/'68s are very similar. However, the stock booster for the '69/'70 Mustangs, with the corresponding (longer) power brake pedal, would obviously be the simplest route to take since it was designed to be a direct fit/bolt in for those bodies.