i know this doesn't answer your question but...

metal is metal and any competent, quality shop should be able to help you. i would be looking for a quality shop first then mopar second. it's usually not hard to tell what kind of work a shop turns out. look at the condition of the shop, the equipment they have, the machining operations they offer and who's running their engines. not that this is etched in stone but it's a start.

it also depends on your level of knowledge. if you're familiar with what modifications and parts are required for your goal than it makes it easier. if you need a shop to spec, machine and build the engine then you would want to lean towards a chrysler shop.

what type of engines are you speaking of?