<... The wastegate lever has very little throw ...>
So why not adjust (shorten) where on the lever you attach your cable

<... only having a couple inches of boost with wastegate open ... I have more than 3 psi ...>
In the context of a wave off or takeoff, 3 psi seems acceptable since it is well within what the engine will handle without damage.  36" on the occasional takeoff or rejected landing won't hurt anything at all, and that's the object of the exercise.
What would enlarging the wastegate involve?  Probably a MAJOR mod for little benefit.

I'm anxious to hear how yours works ... Jim S.
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Jim Sower
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T