That engine comes up just as you and Gary both found, essentially a truck engine that can either be 2 or 4 bolt mains, and either a roller or flat tappet cam. It is not a Vortec, and there are no factory roller rockers that I have ever seen, even in marine applications. Are you sure they ARE roller rockers? Post up a picture, it will be interesting to see.

It looks like they made bazillions of that same engine over that time span. I think the first center bolt valve covers appeared in about 85, but don't hold me to that.

Don