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.

I don't think the driver's side magnum manifold works on A bodies. I did have a magnum manifold on the pass side originally but then switched to a 340 manifold when I bought the Accurate Exhaust Systems kit.

The only thing I could find that works with the Magnum, 4 speed set up was the TTI shorties. I hate headers, and I especially hate long tube headers so I think the TTI shorties will end up being the answer. If anyone can tell me different I'm all ears though!!!