Here is additional information that can be used to confirm the "F54Z" portion of the engine serial number to identify it as being from a passenger car:
Chevrolet Technical Service Bulletin # 291 - Passenger Car and Truck Serial Numbers - Engine Serial # specifics are on page 3 of 5
Inliners.org Engine block casting #s list (3835911 = 1953-55 235 - no specifics as to car or truck)
Your engine casting date code "E 5 4" decodes as E = May (5th month), 5 = 5th day of May, 4 = 1954
Your block casting number "3835911" is found in multiple Chevy Master Parts Books. Below are a few screenshots from some of those books showing this casting code was used in both passenger car and truck applications. The key to confirming what your engine was originally installed in comes from the "F54Z" code stamped into the serial number pad. Per the previously linked GM Heritage Center 1954 resource document, for the engine to have been originally installed in a truck, it would have been stamped with "F54X" for a 3100, "F54XA" for a 3600, or "F54XB" for a 3800 pickup. There is also a screenshot from fellow Bolter
Pre '68 Dave's Blog that provides a ton of detailed engine information which has proved helpful to me and a whole bunch of other fellow Bolters.
I hope this helps to further ID your engine. As has been said by many before, the chance of an engine change over the past 70 years is high but doesn't detract from your truck IMHO.
More to come on the head casting number 3835913.
