I am new to engine replacements, and am replacing my USDM FS engine with a JDM FS motor. It is a 2.0L with an automatic transmission.

I have had numerous issues along the way, but finally got it started only to hear an awful constant screech. I determined that my starter (from the old motor & tested as good at an auto parts store) was grinding against the flexplate after it finished cranking. There are also circular scraping signs on the back of the flexplate near the center, as if it was grinding on the block. This flexplate is from the old motor and was put on the new one according to the JDM store's suggestion.

Thinking the engine block could have some dimensional differences, I then changed flexplates back to what my JDM motor came with. Now, the torque converter studs appear too short to mate to the JDM flexplate, and I have not been able to mate them yet. The JDM flexplate has less depth on the teeth and less overall depth from the center to the teeth outer diameter.

I'm frustrated and running out of time. After a search of this great website, I didn't find someone with the same issue.
Does anyone have ideas/suggestions? Any help would be greatly appreciated. I can provide pictures later if necessary.