I had a "heard a thump" moment on a startup after installing a radiator in front of a brand new 350/TH400 in my '49. Engine locked up solid. Couldn't budge it with a breaker bar on the crank snout bolt.
The flex fan hit the transmission coolant lines. DOH!

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission