MC'oobs? and flea treatments?

I have two neutered toms. They're my little love-monsters. One was neutered about age 8 months, one about 6 months, both the same day. They were both rescued from Out In The World. The older one was about 2 months old and little Calvin was about a month old, a rack of bones and full of fleas. I could touch my thumb and forefinger around his tiny girth, behind his elbows. They're now pushing a year old, mostly indoor kitties who are allowed to go in and out the living room window when the weather is nice and I'm at home to supervise. We live in an apartment and they mostly stay in the enclosed courtyard, close to home. I always call them in before dark and give a spoon of yummy plain yogurt to keep them coming when called. They play like little wild men, ripping and tearing through the apartment, pouncing on each other, rassling, and licking/loving each other.

Even with all the activity, they have MC'oobs! You know when a guy lets himself go to pot, he gets those moobs, or man b**bs? Well these guys have man cat b**bs, or MC'oobs. (assuming Y!A would censor the word) They both have good muscling, I limit their food to 1/4 cup each of Purina Cat Chow Indoor Formula, three times a day, and usually only when they absolutely demand it. I've found that they will play more and harder in the morning if I wait to feed them. Looking at them from the top, they look in good condition. There's a bit of a 'waist' visible in the flanks. Looking at them from the side is another story! They both have this flabby belly hanging down below their flanks.

Panda had started into puberty and started to get that burst of testosterone before neutering, which Calvin missed out on. Panda has more muscle and less MC'oob. Calvin is my snuggle-bear and I can feel his belly muscles toned and tight, but there's this big handful of flabby flesh outside the abdominal muscles, right where a recently nursing dog has a pouch of flabby breast tissue.

I don't think I should feed them less. They are active young cats and they're already hungry several times per day. Calvin has found a new toy that might help - it's a long string hanging from a ceiling light, that's just *almost* within his reach from the bed. He sits on the corner of the bed and reaches up to bat at the string. He was able to get hold of it with his mouth, until he chewed the end off, but he still stands on his hinds and reaches out to play with it.

Any ideas of a special diet food or ways to play with them to get rid of this flabby tissue?

Other question - I heard that the patent has expired on the best spot-on flea treatment, and now you can get the exact same formula at WalMart for a fraction of the price of the original product. What was the name of the brand-name stuff, and what's the name of the new generic? Is it really as good as all that?

Thanks all!