Depends if you want to run the FI or not.
If you are, then it's aftermarket only, it needs to have the pickups for the crank sensor.
SCIENCE FRICTION Billet Steel Flywheel, SFI Quality, 130t/10.5", 360 Magnum, 6-bolt - American Powertrain
If you're not running the factory EFI, then I think any neutral balance flywheel (common=cheap) would suffice, as long as you use the 5.9 mag weight (aftermarket) or have it rebalanced to magnum specs.