Looks like the only V-8 engine options for light duty trucks was 2 versions of the 352. IF it is the original engine, the 4th digit in the VIN would be a "Y" for the 352 or an "8" for a low-compression version of the 352.
Thank you, Sir! Glad it helped. There is a mistake in the '78 manual for the Neutral Safety Switch. The'78 manual shows the NSS attached to the column, as it was in '77 and earlier. That is not the case. On '78 models and later, the NSS is attached to the side of the transmission.