Stuck valves are a common problem on small blocks that have sat for a long time, so remove the covers & oil the valve stems too.
As I was reading through the input I was thinking the same thing. Pre oiling for sure.
I like to spray the cylinders, take the valve covers off and spray the valve train with WD40 or something similar, let it sit a while, and then turn over with a breaker bar slowly, making sure all the valves go up and down.
I've run into a stuck valve more than once; a slant six, a 318 and a 413 now that I think back on this. Good luck and have fun!
