I talk with Frank, have not asked him about this yet. One of the engines he did had a red spring clamp on it. Why I ask first is I saw on Dave Walden's Challenger which had a Keystone.
Bob

Mom & Dad let me buy a brand new 70 Challenger R/T 440 Six-Pack Super Trac Pack when I was 17

(Robert what is a 440 Six-Pack)