As gddyap said its pretty simple. I've been drilling and tapping them since long before there were companies supplying boxes. The one in my bronco I did for a buddy's Jeep in 97 or 98. you just have to drill and tap into both sides of the circuit, decent rams are under $250, its worth buying a ram from PSC, they hold up very well. do not use aluminum fittings, get steel ones from a hydraulic hose shop, they just don't hold up to the cyclic use that we put them through.
If i'm drilling the casting I always do it full of fluid and the system full its messy as hell but all of shavings get pushed back out the hole rather than in the box, done more of them than I can count. all of them worked, some are working 15-20 years later. It only requires an 1/8" pipe tap and a 21/64th drill bit. The easy out is to tap the top cap that bolts on and the end cap but that is not always a safe or practical place. I usually do the body of the housing below the bolted on cap and the channel on the bottom of the box that carries the fluid to the front, it can be tracked down buy the plugged holes from the factory drilling the channel.
