1983 Chevy S-10 header Bolt

Ive done a v8 conversion on my 83 chevy s10, and as I was bolting my headers in today, I ran into an issue. The driver's side bolt which is closest to the front of the truck, which bolts the headers to the head of the block was broken off by the previous owner. As I was trying to drill it out today I drilled too deep, yikes. I was putting pressure behind my drill and then I broke through and could pull the drill bit in and out with ease. Im not too sure what I had drilled into, my best guess is one of the cooling lines, if I follow the line from my thermostat housing is goes straight towards it, but again im not sure. Any ideas about what I hit and what I should do are very appreciated, at this point all I can think of is replacing the head. Thank you in advance, Mike Janos