For the power that your 617 will be putting out, the stock flywheel should be fine. The guys around here have been able to do many performance mods and are still able to use the stock clutch.

__________________
My Primary Driver - '85 300CD - 4-speed conversion, 2.47 rear, lowered, euro headlights, rebuilding (not restoring so much)

Wife's - '08 Saab Sportcombi Aero

Riding a '03 Yamaha Warrior