Keep the two trucks separated and hurry up and sell the 2004 before the Gremlin hops back into the '51!
I am usually right about matters like this...
Seriously, that's the best I got for this mystery. You could take a chance, keep the 2004, and just drive the '51 and see if the noise comes back.
Carl

Last edited by 52Carl; 07/16/2019 1:12 AM.

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