If you need a long block, this engine is in good shape, and it's reasonably priced, by all means DON'T pass it up! Swapping the front cover is no big deal. Just plan on picking up some gaskets and the other supporting parts for the accessory drive if you don't have them already, or factor that into the total cost. You could probably bounce the SN95 parts on Ebay.
You mentioned an '89 convertible. Does it already have a 5.0 that you're replacing? If that's the case, then you can use the parts from the current engine after some clean-up work. I suggest replacing the water pump while you're into it since they're not that expensive and it's much easier to do when things are already apart.