frankenstine car, need some brake help please.

[Sixt5]

65 mustang where the only thing stock is the body.
using what i believe is a 96ish mustang hydroboost unit and master cylinder. i modified my pedal to accept the plunger. running pbr 03 cobra front calipers and a jegs univerasal 9" rear disc kit. im getting a long very soft pedal. after hours of research, trial and error, multiple bleeding using vacuum and the old fashioned way, my last resort is thinking i need a BIGGER bore master cylinder.
im finding mixed information on what the stock (sn95 gt) hydroboost master is so i can decide what to go to. i've seen 15/16 as well as 1".

[Apogee]

Can you be more specific as to the rear calipers? More specifically, the piston diameter/area and type of caliper? Low, soft pedals can be caused by a variety of things including air, pedal ratio, small MC bore, improperly set up parking brake calipers, etc., so the more detailed information you can provide the better.

Tobin
KORE3

[Sixt5]

im unable to get correct information out of jegs at this time but they are by no means a large caliper and is only a 1 piston unit. parking brake isnt hooked up at this point.

[Apogee]

Can you provide a link to the kit on JEG'S website? The help you get is only going to be as good as the information you can provide, and not knowing what you have is going to make troubleshooting the system via the internet more than difficult.