If you can't see the VIN on the block, assuming they used the flywheel that might have been on an engine swap, and your inspection plate is off at the bottom of the bellhousing, you can pull the coil wire and slowly rotate the engine and look for counterweights on the flywheel. An 88 engine and flywheel won't have counterweights.
Some thoughts on a pinned harmonic balancer. There is a rubber cushion between the outer ring and the center hub. That rubber cushion is there to take up shock. If the outer ring is pinned to the center hub, there is nothing to absorb shock. If the shock absorber isn't needed, why didn't they just make a solid harmonic balancer? I'm no automotive engineer, but that's my logic on the subject.