If you want a bike that's totally contemporary, take your '86 Maico and glue some modern plastic on it. No one will be able to tell the difference, except for the fact that it's got a small, strong, and easily weldable steel frame. I just don't get the automatic association that old = uncompetitive. The peak power is roughly the same, while the delivery of power and handling are ranked equal- or superior-to modern standards by many accounts. And, you'll have water cooling, disc brakes, monoshock, etc. The only thing you're missing is a power valve, which doesn't seem to be necessary if you look at the numbers. The only obstacle I see to being competitive on a 25 year-old bike is any rules that might prohibit its use in whatever races you're doing. I have no idea if that's on the books in amateur racing, but I know it is for professional racing.
But, if a large number in the "Year:" line and super-pointy pieces of plastic are worth paying the order of magnitude difference in price between a new bike and an old one, then I recommend getting in line for the new Maico 250. It takes a good engine and turns it into a God engine. 54 horsepower, and reportedly very linear and easy-to-control. You won't be able to have it sitting in a crate in your garage by tomorrow morning, and there is likely a fairly hefty premium over other contemporary 250s, but it's the ultimate weapon in the 250 class. It should be smooth enough on the showroom floor that you won't have to de-tune it, and you'll have as much, if not more peak power than a 450F.