Think 944 porsche. 
We have a lot of experience with the P car brand and a stock 944 lsd out of a 944 turbo S will live a long time @ 300-350 hp. 
Before the team changed to 914's we had a 944 trans/diff that lasted 2 full seasons @ 300hp+ before being freshed. 
All we did at that point was output shaft , bearings and syncros and the syncros were more of a precautionary measure. 
Good luck, 
  
JT