Old fuel will varnish the intake valve stems and cause them to stick. But it looks like you had all of them stick to some degree.
As for the chain slack, it IS excessive; I've pulled out a shot /6 timing chain that had that much slack and retarded cam timing by around 4 degrees. But, as said, we don't know the condition of the cam bearings or if the block has been line bored at some time. The cam is retarded (can bee seen in the pix) but it'll run, albeit with less low-mid RPM throttle response. Hey, it's a $300 truck!
