"Could you recommend a shop east of the Mississippi River?"

...whew...

I have not come across any mention of a dedicated shop for these engines. It seems most have them redone locally. I think in your case, I would look at MARINE machine shops that are familiar with both MARINE and MEL.

If (and when) I have one redone, I will most likely load it up and take to HOLMAN (HOLMAN-MOODY) in Charlotte. Another consideration is Jasper engines. I have talked with their tech people and they seemed knowledgeable enough in them in that they need the Casting I.D. and Date Codes from the engine to research if they have everything needed to rebuild it (as there were so many changes in them the first few years).

About where are you? I am in the WDC METRO.