Just running the outer springs will cause harmonic issues. The inner and out springs have different natural frequencies so they dampen each other. Therefore, I would recommend you buy the correct single spring with dampener for your new cam. check with Lunati.
I think a 2000rpm stall should do it. I would think you could even run the stock converter. Again, check with Lunati.
Why did you select a cam with so much more exhaust duration? Do your new heads have poor flowing exhaust ports?
Good luck keeping that cam from going flat. Those voodoo (lunati) and xtreme (compcams) cams have very aggressive lobes tend to go flat quickly. Sure, they make more power but not worth the damage that a flat lobe can cause.