Quality SB engine builders

Here in Iowa:
Grawmonbecks Competition Engines in Mason City , Iowa They do a great job and are very familiar with Mopars. They have both engine and chassis dynos.
https://www.facebook.com/Grawmondbecks/

Mid America Racing Engines. in Washington, Iowa Dave is all Mopar and has competed many times in the Mopar Muscle engine competitions.
Mid America Racing Engines | WASHINGTON, IA 52353

R&J Performance Enterprises Cedar Falls, Iowa Radar is Mr. Mopar when it comes to heads. He has worked for Gary Ostrich and did experimental work for Chrysler Corp. as well as r&d for the B1 heads and John Force. They specialize in heads but they build many complete engines.