Wow, the things I miss watching the stupid superbowl. My wife had to pick me up off the floor and set my chair back up.
I have not heard of a valve cover coming lose, but I personally have blowen apart 3 mufflers from tune ups or getting trucks started after years of no use. The last one was last spring getting my 73 k5 going. Damn mice building nest.
As far as the other two, my step father andI where replacing header gaskets and he tried to start the van prior to hooking up the driver side sparkplugs. After it started and ran rough (ya think) he shut it down and put the boots back on. Well it must have super loaded raw fuel into the drivers side exaust and when started again boom. Cool looking clamshell.
As for number three, new motor install and dist. was 180 out. also loaded the motor after the backfire we needed new muff and tried to set the hood isulation on fire. Lucky no one was looking down carb.
So my questions return to timing and /or sparkplug wires mixed up (chamber firing when intake valve is open). Or is valve not seating and is it loading into head. would explain the miss.
Before I forget, I cant remember what year it started but on my 90 with TBI you need to cut the wire (brown?) in order to set the timing with the ECM. Something to do with the spark advance. I dont know why, but that is why I make best friends with real mechanics. There may be a post about it on here somewhere. Sorry about the valve cover.