Toyota Repair: Previa engine died, spark plug wires, timing chain

Question
Hello
My wife was driving our '91 Previa last night when it backfired once, then died.  She was travelling at about 35-40 MPH.

I have had the van since new and never had any engine problems. It has 260K miles.

The backfire makes me suspect a timing issue, which leads me to think that maybe the timing chain broke. I have never had the timing chain replaced.

Your thoughts?

Answer
If the timing chain broke, it would be the first one that I have ever heard of breaking, if this should be the case the valves are probably damaged and you are looking at major engine problems.
It's more likely that it may be an ignition issue, check the spark plug wires and the distributor cap and rotor, it could also be a distributor or igniter problem.
How does the engine sound when cranking it, does it sound normal, if the chain broke you won't be able to crank the engine it will lock up.