Not a warbow guy, but I do know a bit about strength training. It would be a mistake to work out only by drawing bows especially at the level of 100 plus pound draw weights. Drawing a bow is not a balanced workout. It works a certain group of muscles in a certain direction, and if that is all you do, your muscles will develop in an unbalanced manner. This sets you up for potential injury.
Drawing a bow of that weight takes most of your upper body to do properly, primarily your arms, and upper back, but also your shoulders, chest and core. You should work them all in a balanced manner. Do not neglect the lower back and abs. A good strong core will prevent injury and you'd be surprised at how much an good core can improve your overall strength. I'd recommend putting together a program that works all you major upper body groups, but with an emphasis on your arms back and chest.
Were I in your shoes, training for a heavyweight bow, I'd speak to a personal trainer and put together a workout regime. But if you don't want to do that you could put a program together yourself, just make sure you aren't ignoring any of your groups. Its easy to forget some of those smaller muscles, but they are important too.