Welcome to our nightmare!!. As I've said, there is a similar thread on the UK Twinshock forum.
Here in Qld we have had 500cc singles running for many years as that was a good cheap way of starting in the sport. All of them were home built so there must be precidence there.
I can also remember racing against Murray Williams on a CR480 at ACUSA park in what must have been 1983 at the Nationals. I remember it well as Murray ran with telos on the front and though it was quick, it was all over the place, and also it was the year we pulled the front end off the DR500 we raced-and that proves the point about strengthening the frames at the head stem.
These outfits-500 4stroke singles- are a top way of joining sidecars, they are easy to build, fun to race and cheap to maintain. They can be era correct if you pick the right motor, Honda, Yamaha, Suzuki all made one as well as Husky and maybe even the LC4 can fit in. Rotax also had one but I don't think they ever had one here. For that real retro look you could even try something from the speedway/dirt track side like an Eso or Jawa and bolt it to an AMC box.
I can't see why they wouldn't let you race and if we got enough 500s we could race two classes again.
A good 500 4 stroke can make 50hp and is light enough to win on when ridden well. They make for great racing, which we need and can be used to train more combatants, which we need and it's cheap, which is good, and they raced in the day which is great.
Also the 500 Yamaha we have up here is a copy of an early Wasp that Alan Hill imported in the early 70's .....they made 4 or 5 copies of which this is the last known surviver and we had to rebuild the chair as it had almost rusted off. I can't see why it's not a pre 75. The only problem is the sidecar guard which is later model as that's all they had to copy.
