Before you do anything, let's discuss some options. Have you considered a turbo on the 350? Have you considered an engine swap to an LS motor?
Here's a for-instance turbo kit.....
https://www.amazon.com/XS-Power-High...ag=d_2b_a_p-20
And an LS motor complete with transmission, less EFI could be had for $800-$1200. Add a manifold and carb.

Budget $600 for a decent 10" torque converter.
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