Typically, Clarks shared the same bellhousing patterns as the standard 1/2 ton and up trucks. You should be able to bolt up to a bellhousing that had a SM420 behind it which was common in 1956. You will need to get the bellhousing that is correct for your motor (six or eight cylinder). Clarks usually were put behind chevy motors in the bigger trucks, and since GM standardized everything possible, yours should bolt right up.