Actually I believe if you look at the history of the Camaro what killed the Camaro and Firebird had nothing to do with its powerplant it was all design and functionality. When the Mustang looked like a dressed up Pinto in '74 - '78 everyone(including me) thought it looked like a joke. The Camaro stayed to its own and stayed big, power is in straight lines concept(let the owner tweak up the bottle neck offered at the stealership, mod away).
In other words the Mustang took the redesign hit when they could afford a cultural change during the gas crisis, Camaro design missed its opportunity. Over the long haul the Mustangs ability to adapt and be accepted as a Pinto in a miniskirt during the gas crunch allowed the '79 and laters to stay small and nimble(just not enough power). No drastic design changes. The weak spot for Chevy was never its engines for sure, it was design. The Camaro and Firebird stayed larger, less nimble and looked more like big darts with wheels. The Mustangs name, balance, and nimble footed stance allowed it survive. It better fit the times. The Camaro was on a slippery slope from '74 on(IMO), I'm actually surprised it lasted as long as it did. The IROC postponed the end and gave it a second gasp but the nimble agility(day to day daily fun factor) of the Mustang is what bought sales.
Chevy was very fortunate in 1955 to come up with a ground breaking design that would carry them a long way.
http://www.cdps.k12.ms.us/chs/eric/eric.htm
Interesting to read up on that motor if you are ever curious. Back on topic, I would not count the Camaro out - Chevy may not make that mistake twice. I think the Camaro could not redesign because the fanboyz would not accept a small nimble Camaro(cultural changes are rough). The Camaro didn't lose for good, it just went into the penalty box for a makeover. To verify what I'm saying here look at the physical dimensions of the last Camaro and the Mustang of that same year. The only comparison is they are both RWD American cars. If you've driven both the Camaro and Firebird they feel like the front end you can't see is always half a block in front of you waiting to get clipped off and if you ride in the back its like a wild-west wagon ride(strap in - bumps sukz).
The Mustang was nimble and sure footed in comparison. Imports bring a different challenge, but for the Mustang they should ignore imports and worry about Chevy's return to the game. Hope they(Ford) are ready. I think we agree that there is more than the engine size, I feel Chevy's engine just kept them in the running to extend the Camaro's life. It was IMO Camaro's design disadvantage as a complete car that destined it to fail, the engine kept it alive longer. I think there is a lot of potential for the new '05 Mustang body style, I look forward to see what direction Ford takes it....
Sidenote: If you ever want to check out something funny IMO, take a good look at the interior design and instrumentation of the '68 Camaro and its inboard style head lights - then look at the '71 interior design and intrumentation and in board tail lights. Seems like from '70 - '71 Ford and Chevy swapped designs a little. Why we'll never know. Furtunately in '74 Ford woke up a little, both Camaro and Mustang interiors seemed to use a similar motif.