Bummed Out!

[Libertad]

Just when I thought I had the mechanical stuff done with and I was getting ready to lower my 75' C10 LWB in the coming weeks now this happens:

I was driving to work last night and my motor made a rough growling noise with shaking and white smoke out of the exhaust then it died on me, just prior to that it sounded like a push rod was ticking and my oil pressure went down. Once on the side of the road it wouldn't crank over anymore. I had to leave it there and had it towed home this morning. I haven't been able to look at it yet.
The motor never leaked oil and just recently I noticed what seemed to be a rod knocking every once in a while that would last for a minute and then go away.

Where should I start looking for what went wrong. I have come to the realization that I may have to rebuild the motor or maybe find another 350 to drop in there but could it be anything external. Any advice on where to start is appreciated.