Switching to rear disc brake question

[CnDRacing]

I'm switching to rear disc on a Ford 7.5, using the weld on brackets and GM calipers. Which master cylinder should I use? Currently have a 87-93 mustang unit (aluminum w/plastic resivor) Should I remove the proportioning valve?

Thanks

[exfordtech]

i have a mini with a ford 8" rear that had drum breaks that was converted to discs. whoever built it used the stock master cylinder & proportioning valve. i felt it had too much rear break so I added an adjustable proportioning valve. I am a lot happier now. I feel like it finally locks up the left front when I want it too.
Yes, I race on dirt.