Their are two 318 Detroit’s the 318 HP 8V-71 and the 318 CID 6V-53 I am guessing that the C-90 came with a 6V-53. The 8V-71 is a good size chunk of iron and fit very tightly in the biggest of class-8 trucks. If it did come with an 8V-71 an 8V-92 Silver would be an easy swap and it was 425 HP.
