ran into that myself this spring. Started up the srt and it sounded like rocks rattling around till the injectors pumped up. I thought the motor was going to come apart. Ive stored newer vettes like that and never had this happen so im guessing the hemis have a different type lifter that tends to drain down. I know next winter ill be starting mine every couple weeks. Probably the same reason hemis lifters tend to go and many people get the hemi tick.This is normal for a car that has sat for 3 months IMO.
Even though my Firehawks are basically garage queens, I try to start them at least once a month even if I don't drive them. Let come up to temperature, rev the engine a little and shut down.
Even doing that I try to roll the tires every 2-3 months at most.