70 K member in a 66 Dart

Welcome to the board Robert. The answer to your question is NO. The 66 was the last year of the narrow A body engine compartments, and in 67 they were widened so anything newer than 1966 is too wide for your car. Is there something wrong with the K-member from your 66 or were you just planning an upgrade? In case you were just planning to put a V8 to replace a /6, then the 66 K-member is the same for both 6 and 8 cylinder engines.