You are mistaken the Falcon DID NOT have a suspension design ANYWHERE NEAR the Mustang II, it was the same as the MUSTANG of the same year! The first series Mustang and Falcon (64-66) were built on the same "platform" and in fact the Mustang "Mules" that Ford drove around to test Mustang designs were Falcons with some Mustang sheetmetal looking like a half breed.
The early Mustang Falcon had the coil spring mounted on the UPPER control arm going UP to the TOP of the apron right under the hood.
They are NOT any way even close to the Mustang II design, sorry NOTHING will enterchange.
Now, to switch to five lug, simply put Mustang V8 front hubs and a rear axle and there you will have it. The 6 cyl had four lug the 8 had five lug.