Rufus
I'll throw in some random ideas as a starter:
Fuel pump relay seems like a good guess to me, however your model year has a so called MAS unit that integrates the fuel pump relay, with, I believe, the KLIMA relay. It is much more pricey, but can be have used at a good price. However it does not seem to fail as often as the fuel pump relay.
When the car does not stall, does it run ok? How is the fuel consumption?
Have you checked secondary ignition (especially distributor and rotor!)?
You can also measure duty cycle to get an idea about the mixture adjustment electronic (
http://www.landiss.com/mixture.htm).
There are two fuel pumps in tandem on the car - you could measure voltage and current. Also, how old is the fuel filter?
Good luck, Bruno