If you need it, I can give you some advice for Raikou and Entei. I caught both without Master Balls and yes, it took me a while.
If you take someone with Mean Look (you know that I'm sure) and an automatic HP-restoring move like Ingrain (by now which I recommend taking Smeargle, which can Sketch both moves), it can plant itself and even Roar will not end battle.
With yourself firmly planted, you just need to False Swipe down to the final 1 HP (I don't recommend planting yourself for the first couple of encounters for this reason, but weaken and either paralyze or force asleep during those). After that, luck comes into effect as you need to try to catch it in your Ultra Balls. It took me forever, but I didn't have the Ingrain move and my Entei was paralyzed, meaning I had extreme luck of paralysis affecting Entei when it tried to Roar at me. After about ten turns, I managed to snag it. Problem solved.
Ho-oh? I cloned my Master Ball and took it to capture Ho-oh. Lv.70 and I was highest 55 at the time. No chance otherwise. :D