Inliners International Forums General Discussion Engines Specs needed for a Chevy I6 (cast # GM 3877178)

Hi, I found the serial #, F0403FY. Can someone decode this for me?

It's possible we could not be cranking it correctly. This is my first hands on restoration; I got the van in exchange for a laptop and we plan on using it as a gear van for some music gigs. I have a few people with automotive experience but could use any protips this community can throw at me. I really want to avoid taking the engine apart as I'm on a small budget. I'll retest the cylinders tomorrow evening.

Edit: I have my father (jet engine mechanic as of late, used to be car mechanic), a friend in an automotive class, another friend who took a bunch of auto classes, and an acquaintance who restores classic cars.