Alot of good advice here. At 6'4", 180 lbs. is still going to be skinny though. I'm 6' even, and at 215 most people can't even tell I work out when I'm dressed! If you put on 15 pounds of muscle, with a proportionate strength gain, your power is gonna sky rocket, but your looks won't change much.
Don't worry about being "too heavy" either. Your muscle is going to be able to carry it's own wieght many times over. In fact, you might even "feel" lighter. If CD is a 200 lb. bodybuilder, he's gotta be like 5'2"!
You want to concentrate on big multi joint movements for maximal testosterone boosting/functional kung fu strength. I've been powerlifting for about three years, and I found the following workout to be effective in my off season. It should work well for strength/wieght gain in an internal art.
Bench Press/Cable Rows
Squats/ Deadlifts
Dips/Chin ups*
Superset each pair (performing them back to back, with a rest between each pair). For power gain, work 3 sets of the heaviest weight you can handle for 5 reps. Since size is your goal, you can do 3 sets of 8-10, upping the poundage whenever you push beyond 10. For a real kick, I like to work for power AND size by doing 5 sets of 5 reps.
Do the routine twice a week, with at least two days off between each session. Oh, and I forgot to mention that the pair marked * is a "burnout phase" working the muscles you did in the first session to get a maximal pump. You needn't do the burnout pair unless you want to put on size, but then again, it can't hurt, right? You may also want to choose a burnout exercise for your legs too. I don't like to because Ba Gua sessions tax my legs enough as it is
" You must use your Dan Tien, spine, ligaments, tendons, joints, muscles, and chi for power. Your whole body together, not seperate parts. If you don't, you are not practicing Ba Gua Chang, you are practicing Ba Gua Bullsh*t." - Master George Xu