if it dies after about 30 minutes with no spark on an 87
then its probably a short... you probably have a bad coil or coil
wire and its dieing after it heats up....if only one plug was dieing this
car would run with 5 cylinders.. so its not in the distributor or
spark plug wires... the only other option is that the coil delivers
spark to the distributor...

for an electrical part to die once it heats up is not unusal...