Installing a remote master cylinder to work with the Biltwell forward controls is actually quite simple.
Using the right stuff, you will be able to eliminate that ugly master cylinder placement found commonly with other forward control sets.
I used a late 87- 03 Sportster master cylinder that has a plunger style that accepts a treaded 5/16 x 24 stud ( I used a piece of 5/16 stainless round stock and cut and threaded it to length). Other master cylinders I found had a clevis style ends. I avoided them because I wanted a simple and direct linkage to the plunger so that the applied pressure was more direct. At the pedal end, I used a small ball joint to connect the treaded stainless push rod to the pedal. The beauty of using one of these little ball joints is that it will allow the linkage to still work properly if the alignment is off a bit (but still attempt to get it as level and in line as possible).
With the foot pedal installed and the stainless rod threaded into the ball joint, and the ball joint attached to the pedal, look to see where on the frame the bracketed needs to be welded onto the frame so the linkage will all line up. Actually take the master cylinder in your hand and hold it where it it needs to go. With the threaded stock and the ball joint attached to the pedal, hold the master cylinder against the frame and draw a line with a marker just underneath where it needs to be welded so that the push rod will be inline with the plunger of the master cylinder.
With the line in place, begin to make a template out of cardboard so that you can transfer over the shape needed to the 1/4 steel used to make the bracket to mount the master cylinder. The bracket is super simple. All it really needs to be is beefy enough to weld to the frame and accurately except the 2 holes in the master cylinder. Be sure to double check that you can still pull the engine and transmission after you weld the bracket on. As you can see, I placed mine between the engine and trans with enough room to yank them both. As a tip, see what lengths of brake line is available to you. It might be a good idea to move your master cylinder a bit if you can as to avoid having extra or too little brake line when you go to plumb the system.
Cut and thread the push rod linkage to length leaving some room to tread the push rod in or out for some adjustment. Hang your caliper, determine the length of the brake line needed. Bleed it though and you are done!
It's really that easy.
Like I said, just do your best to line it up and make sure that everything around it will clear and you'll be golden.