most boost I can get out of her at 3500 rpm is just shy of 15psi

I already checked with IH and found that they did not set up their exhaust the same way that Ford did. Thanks for the heads up on the up pipes, I never would have figured that one out.
My injectors are all AA code.

 

You can try some chevy 350cc header dougnuts, they are a bit thicker and work sometimes. Otherwise you have to replace the up pipes.