Personally, I'd be (and hope soon to be) looking for a Magnum Maico, that is, a '78-79 model year. They don't have the crazy power of the 490 but they're a little lower to the ground and I hear you can really tell it in the handling. If you're not too concerned with racing vintage, you might try a monoshock Maico of '82 or '83. The '82 is also a 490 and the motor is virtually identical (it's ported to emphasize low-end slightly) but it just happens to be a monoshock. These bikes got an incredibly bad reputation when some weird design work resulted in bent shocks, and Maico lost a trainload of cash on warranty claims. The '83 bike has an even worse reputation. Even though it makes the sort of power than an '81 or '82 could never dream of, and the shock problem was fixed, the bike's transmissions sometimes weren't heat-treated (this was an act of sabotage, not failed QC.) Some 490s had their transmissions blow up and some people were even killed. If you find one today, the problem is 99% sure to be fixed, and the bad rap keeps the prices lower than an '81. Unfortunately, many vintage racing series' don't allow monoshocks into competition, which means that you may not be able to race this bike, and that further drives the prices down due to decreased demand. My monoshock recommendation is the '83 Sand Spider (the Sand-Spider is the 5-speed, and apparently Super Hunky helped name it!)
So there you go.