Sometimes it's the easy things: How did you set the valve lash? There's the way some people do it by spinning the pushrod of the rocker you're just setting between your fingers til you feel a slight resistance, then add half a turn.
If you use new lifters, which have no oil in them, then all that would cause the resistance is a small spring inside the lifters. That isn't always recognised as "enough resistance" and the rocker nut is screwed down til the lifter bottoms out. This way the valves will allways be held slightly open. This usually robs some power, but the engine will run. The drivetrain will fatigue very fast though and if you happened to make this mistake on a couple of cylinders then it's a sure way to wreck a lot inside an engine. Because of the fatigue of parts when one goes others which are going to go soon will go at the same time as a side effect with the added stress of vibration and metal shavings in the engine.
Post some pics and we'll possibly be able to tell you more (besides it would make an interesting pic to see anyhow...)
A Rod bolt going could break your lifters, if the crankshaft turned further and smashed the big end of the broken rod against the cam shaft. If the cam goes out you have the same effect as if your timing chain breaks: some valves are held open and the pistons smash against them from underneath, that'll almost certainly leave you no reusable parts in the whole short block, heads are most probably at least bent if not cracked, crank needs thorough inspection.
But as I say, where aiming in the dark here, it's all "could bes" and "I thinks" but no "that was a...".
Maybe this helped you none the less, but with a couple of pics there'll be more to say I guess.
GL,
Max