Magnum Swap Checklist...... this is a long one.....

Everything i read, including replacement piston specs shows the piston will be over .050 in the hole. If you are sticking with stock stroke parts, a good stock damper is enough. Racing regularly with a lot more rpm and i would consider upgrading.
Have you considered 92 year Magnum exhaust manifolds? I understand they have a good sized outlet and flow as well as 340 manifolds.