With regard to the 600 Open Class:  Paul has completely opened up the motor with the following exceptions:

#1 Must be stock bore and stroke
#2 Must have working clutch
#3 Must be self starting

If your bottom end is NOT stock you must have a minimum weight of 800 lbs.  If you have a stock bottom end, (basically last years rules), the minimum weight is 775 lbs and the motor will need to be tech'd and sealed like last year. 

He has not finalized the 600 restricted rules but I believe they are going to have to be completely stock top and bottom end.

1200 rules are not finalized either but he is considering opening up the bottom end of those to some degree as well (e.g., remove the gears from the transmission).

As for Clay Cup I am not sure if he will lower the 600 Open weights to 750 and 775 or if he will keep them the same.  I suppose he could also allow multi's but I'm sure he would make them weigh even more.

Hope that helps.

I have heard he is considering allowing the 1200's to remove gears from the transmission.  Other than that I believe they will remain the same as last year.