Andy,
The tranny used in the 2gen NA's is essentially the same as those used in the first gens. Mazda considered them at the limit with 160hp at the FW. They used a beefier tranny with the turbo cars that had a 200hp FW rating.
When you consider that your team's cars are probably pushing 200+ at the FW,running 4.88 rearends,and pushing in excess of 7000rpms most of the time, the stock box is likely to break!
A rebuilt/blueprinted tranny with a trued and balanced(for high rpm) driveshaft may be the best you can do. A good synthetic oil( Redline MTL in my book) will offer the best lubrication, lowest temps,and the least frictional loss, but the mechanicals have to be spot on!
Good luck,hope to see you guys in June
B