What do shot timing gears sound/act like?

[alden]

I'd like to find a diagnosis method without opening up front of the engine FYI - the engine is a 235 in a 59 Apache.

We attempted to set my dwell/timing this weekend, first by changing out my distributor only to find that the new one wouldn't fire, so we went back to the old one. At various points in time the truck would run but not great, now it won't start at all (I went through the steps laid out by several posters on stovebolt explaining how to put the distributor in). I tried checking the timing by using the ball on the flywheel lined up to the pin but I couldn't see the ball to save my life. Eventually gave up that route and marked the pully for the fan and a spot on the block and tried checking the timing with that. The marks only lined up 1-2 times out of maybe 10 rotations. The most significant result I can get by cranking the engine is a loud single backfire after several seconds of cranking; I know the plugs are getting a spark and the carb is getting fuel. My neighbor is convinced that the timing gears are shot but it seems a bit odd to me that the truck could go from running (albeit roughly) to not even starting in such a short span of time so I'm posing this question to you, any ideas what the problem might be?

Thanks!
Alden