I have also toyed with the idea of putting my old school Acoms 27mhz electronics in the RC10, but the thought of the long aerial and messing with crystals is just a step too far...
I have found the web site I was thinking of (other than the oOple RC10 class that Josh posted about above) - click through and have a look:
http://revival.a1racingclub.com/classic-racing.html
There is too much to cut and paste, however:
I couldn't see a motor limit...
But they are grouping cars by age... Scroll down and look at the cars list for each group...
And they have 'nostalgia points' for those using brushed motors, old school tx/rx, NiMH/NiCd etc..
Mostly appropriate for a big meet with lots of folks, but might be some useful ideas there, for example the RC10 Worlds is two 'age' classes above the classic, as it's transmission etc. is quite different.
Looking forward to getting some classic track time during practice on Thursday (I've got the sticks back to use with the cars too Matt!), and hopefully the wheels and carpet tyres for the Classic will have arrived by then...
Barry