Your 380SL has KE-Jetronic which is basically a mechanical injection system.

This book goes deeper than my tiny brain can follow. It’s not a diagnostic guide for every configuration but it’ll help you figure out what to try next.

https://www.amazon.com/Bosch-Fuel-Injection-Engine-Management/dp/0837603005

Nice find on the 170! I wonder if you’d be better served by an OM601 than a 616. If you’re really creative, cut the body off a 201 190D and set the 170 body on it. I don’t know if the 170s hood and fenders will go over the 201’s upper suspension attachments.

Here’s some beefier parts for you - https://sacramento.craigslist.org/pts/d/mercedes-benz/6745473204.html

Sixto
98 E320s sedan and wagon
02 C320 wagon