I know-- I googled the number on the driver's side, right next to the bell housin (57L GSGI), and got a very wide range of responses.

I googled the number on the passenger side, and I also get varried info-- some sites say it is from an 87-92 truck, others say it is from an 87-88 camero (which would make it an L98 motor).

I'll also add that valve covers on this motor have the bolts in the middle (as opposed to around the edges), which is also consistent with an L98.