James, Wally Wasp is being a bit nit-picky there with his post.
The 3 major classes we run are pre68, pre75 & pre85.
Mostly early sidecars for motocross are based on the Wasp chassis from England, if genuine they have a chassis number stamped on the steering head i.e RT2 RT15 etc...
In pre68 class the regs say it can be an RT2 or must be based on a road frame with a sidecar attached.....the sidecar must fit into the regs or 'moms' in the rule book, read up on them before firing up the hotsaw and welder.
pre75 is usually all Wasps or home-builts based very closely on them, because they work, but there is a rub....many '76 model Wasps (RT15s) are closer to the old model and so far from even a 78 or 79 model EML that they are outclassed and so really belong in the earlier catagory. As many run Norton, Triump or XS Yamaha engines that fit better into the older class too.
Your '85 Kawa is just out of the pre85 class but could be considered a "carry over" model if that engine was built the same before '85 and has no changes like flat slide carbs.
You then end up in the pre90 class and up against the lightweights like CR500, KX500, Maico 490, KTM 520 etc...power to weight will beat you.
Look, it all depends on your fun factor requirements, if you just want to have a ball, go at it, just bare in mind that if you want to run a National title of even a State champs, you might find yourself chucked in with the fast guys on quick outfits.
It would be a good idea to put your boy on another sidecar sometime so he can get a better idea of what is really required....we have had too many guys buy a sidecar that they can't learn to ride because niether driver nor passenger have a clue what's going on
