C10 Leak/Start issues

[IndifferentJester]

Been awhile since I've posted due to deployments and finally have some free time to drive my truck around. Have two issues that I'm trying to fix and maybe one of you can help me out. My truck sat for about a year and ran fine just before it sat. It cranks just fine but never turns over. I've put new fuel in, checked the spark plugs (fairly clean and still look new), and ensured everything wasn't flooded. After doing my checks I noticed my coolant was low so I began filling that up. Came across something that looked out of place. From (what I think is a casting hole) in the engine block, my coolant was pouring out like a stream. It's on the driver's side, near the rear spark plug. Coolant just continued to pour out and with my very limited knowledge with engines, it seems like a cap should go there (and I faintly remember one being there). Am I wrong? Any thoughts on why my engine won't turn over? Thanks.