It is entierly possible that two valves have stuck open over the winter, depending on a couple of things. What was the condition of the oil before it was put to rest?
The reason two (at least) would stick is simple. Both of these are at the back of the head, where the oil is going to drain and settle. Older oil can solidify a little, particually with a bit of moisture, and can form a thick gunk along the shaft of the valve. This will cause the valve to stick open, and could very well bend pushrods when the engine is fired up again.
Granted, this is assuming a couple of things. 1, the oil is old and dirty, and 2, the valve seals let a bit of oil through.
I have seen this before on an older 454, but that was an engine that sat for some 4 years before they tried to fire it off again. Ended up having to pull the head and dissassemble it to scrape the built up crap off of the valve shafts before it would run without popping or bending pushrods again.