the winter before last, my timing belt broke and left me with 4 bent valves. i went and had a valve job done and the head cleaned up. i also changed all seals and gaskets fromt he head gasket up. for some reason, it didnt even dawn on me to give it a break in period after doing tis and i just drove it normally. within a week or two, my radiator cracked and had to be replaced, but i think this may have had something to do with the fact that my fan motor was going bad. a couple weeks later, a spark plug popped out while i was on the highway. i heard a loud pop, pulled over and opened the hood, and there was the plug dangling from the wire sparking away. about 30,000 miles later, i was driving on the highway and i hear a pop with a knocking sound that slowly got louder and louder. by the time i got to where i could pull over and get out to check it, i had flames under the car that eventually went out on their own. i got the car towed home and started tearing it down. i found an 8 x 6 inch hole in the side of my engine block, and i guess the flames were from the oil pouring straight out onto the exhaust manifold. though the car would still start, run, and drive. so, here are the questions:

why did this happen? was it because i didnt give the car a break in period right after all the headwork? was it because the head was like new while the lower half of the engine had no work done to it, so it just wasnt able to keep up (keep in mind the car has 400,000 miles on it)? was something done wrong when i had the valve job done? or was it just time for it to happen?

why did the spark plug pop out on its own? was it just not tightened down enough, or was there too much pressure inside the engine forcing it out for some reason?

is it possible that when i threw the rod that more valves were bent?
im wanting to know this, because im planning getting a new block from the junkyard and doing a tear down and rebuild on it and im trying to figure out if the head will be ok.