Wayne

I can suggest that Raplh can and will make a custom carb adapter as you mention that will rotate the carb to any position you desire...

Are you using a programmable radio? If so take a look at the throttle curve. The problem you describe is pretty common in that the transition is non linear with most gassers. I typically have to tailor a throttle curve for most of my gasser's to achieve a balanced linear transition...

Your carb needles may also need attention.

Is your servo arm and bellcrank arm pivot the same length? Is your servo centered when the carb is open half way or centered? Both of these items will effect the ratio or geometry of the linkage and cause some problems unequal movement...