You can fit the coilovers on there....it just takes some work. Check out Dan's truck its the same as yours I just came up with this idea:
Those were still in progress pics...we also ran a support off the other one where its missing in the pic and also we ran more tubes off those mounts down to the frame and other spots. Thats just a general refrence idea how you can make it work.
You don't want to change the master cylinder anyway it will affect your braking in a major way. All the braking power as well as the front to rear balance comes from the relationship between the volume of the master cylinder to the volume of the wheel cylinders. Smaller master cylinder will give more clamping pressure at the wheel cylinders, for a given pedal pressure, at the expense of pedal travel which a Toyota really doesn't have to give up. We used Willwood's reverse pedal assembly mounted inside the truck, which was a PITA to mount, and it was very hard to get the brake balance front to rear. Giving up the power brakes lost us about 20%-30% of the braking power of the truck. Curt
If giving up the vacuum boost cost you braking performance in a truck that light you need to change the m/c bore sizes. There is no reason you can't have brakes at least as good as stock if not superior to stock.
What calipers are you running [piston size(s)] and what are the m/c bore sizes ?
I used swerve around my halucinations, now I drive right thru them.