Breathing new life into the 318 in the Scamp!
Dave,
I had a heigth issue one time using a MP high volume pump, the body is taller.
Maybe you recieved a HV pump that was packaged wrong.
The stock Mellings standard pump clears every stock oil pan that I have ever seen.
MY stock 340 pan has a slightly raised area to clear the pump body, so checking the 340 pan will not do you much good.
If the pump checks out ok, I would just modify the pan to fit, or try the Mellings pump.
http://www.summitracing.com/parts/mel-m72/overview/make/dodge