A:Answer I have figured out the answer to my question above. The LG microwave, model LMC 2075, fits perfectly into my 14 year old trim kit GE JX 1830. It looks like it was made for it!
Be sure to retrieve the left side vent piece which is screwed onto the old microwave (part of the trim kit). This piece also screws perfectly onto the Left side of the LG microwave.
If someone had told me this, it would have saved me from hours of searching and talking with Best Buy salesmen and chatting online. I do hope my response will be added to the question and answers online.