Help with dampener ID

Wow thanks for offering to post pic Kernel S. That's why I love this site, everyone is willing to go the extra mile to help others and the knowledge base is awesome. I am very familiar with the latter dampeners with the slot in the outer ring for balancing but this one kept saying 340 to me. Since I already have a couple of complete sets of pulleys for the later style I'll probably invest in a compatible dampener. Anyone got suggestions? Motor is in the 425-450 hp & torque range w/4 speed. Not planing to race it but will hammer on it every chance I get.