I did some research over on fordfe.com on the S code and "in some cases, not all" the block will have the cross-bolt pedestals, bosses and a side oiler gallery casting. I see that the block does have the cross-bolt pedestals, couldn't tell on the cross bolt-bosses and
oil gallerythough. I also see that there have been some 390 "S'" code blocks too.
All in all it appears to be a valuable chunk-o-iron and definately worth doing the research and rebuilding. Great find!!
Dave