Great info there Werby.
The 1000 would rule out way too many cars. A 427 Ford in anything after 64, even 61 Meteor wagons would be out and what a fearsome musclecar that 332 was , eh?
It is quite the shocker that Buick, Olds and AMC are more prevalent in that series than Fords! I would think several different models should be competitive, the obvious 428CJ's but 427 Fairlanes and Comets, and Boss 429's. I don't think any 289 or 30, even a Boss would be able to run with the big blocks unless they allow Tigers, Cobras and TVR Griffiths.