Nice slider, but what I see is a really nice track!
I agree with much that has been said about the sliders and of course in the mid to late 70s they were king. The emergence of both oiled tracks and the fast and well braked 500 2Ts meant that they didn't get the game all their own way, but there were still quite a few guys riding them even into the late 80s.
My question though was more around the MX framed bikes and why we don't see more CR/KX500s with 19" wheels in vintage DT. If I had the spare cash, I'd really like to build a good CR250/500 with the old school wheel/tyre combo. I wouldn't be quick, but it'd be neat to see a bike more representative of the state of the art in 1984 or so.
The guy I mentioned earlier who raced an XR600 still has it and keeps threatening to bring it out for a ride, but he hasn't yet. I hope he does one day just for the novelty value. We were talking wheels and tyres too and we still wonder why the 18/19" wheels and tyres aren't more common today as well. Again, is it the deco tracks? I'd have thought that if 18/19" wheels and tyres worked back then they should do so today, but most modern racers seem to favour the 21/18" combo with a knobby front and Michelin trials rear. I have that on my modern YZ125, but that IS after all a 125. You'd imagine a 450 would overpower those tyres. Although as has been observed over on OzDirtTrack, the modern guys tend to slide their bikes more than was the rule BITD.