You can use the existing pedal support, but you will need several pieces from a clutch pedal support to swap over (pedals, clutch pedal stop, spring, spring brackets, etc.). I suggest you locate a complete pedal support from a stick shift car and use the parts from it on your existing automatic support. Almost all the used manual pedal supports I've seen are tweaked from the forces involved in working the archaic Mustang clutch linkage. Your automatic one is probably in good shape.
Remember to get new pedal bushings and the little Delrin clips to insulate the ends of the big spring.
As for the Z-bar, I believe they are the same for 6 cyl and V8 cars, and the only oddball was for the K codes. There was a difference in the '65 and '66 versions, though, so you will need to get the one that matches your clutch equalizer rod.
It's been awhile since I did this conversion, so I hope I'm getting all this right. If anybody knows differently, please chime in . . .
"When a woman is a really good driver, she is just about perfect."
- Raymond Chandler
'66 GT Fastback show car, nightmist blue, warmed up original 289 & T-5Z, 3.80 trac-loc, AC, PS, pony interior, Retrosound, rally pac
'66 Coupe driver, Bullitt green, 302HO w/ 351W heads, roller rockers, Holley 600, T-5Z, 3.55 trac-loc, collapsible column, tank armor, disk brakes, shoulder belts
'11 BMW 335i X-drive, 6 speed manual, all the bells and whistles