Yes, the 5296 would mean it's the 4296th engine off the assembly line. No information on the "I" though.
I think it's possible that the front engine plate had holes for both car and truck mounting, simplifying part inventory, but your son may be right about holes being drilled for mounting in the truck.


Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.