Not too sure by the photo of the engine, but, if that's a V6 - with those mods, I reckon the power you have is the mods compensating for a duff vis motor or 2.
So really - I reckon - you have decent power. Check the operation of the vis motors and you'll find 15-20 bhp if they are not working.
Now - I'm no guru - just a thought.
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