white/grey smoke is usually a sign of retarded timing.
That can be caused by air in the system because the fuel pressure is used to push the advance piston. It could also be a problem with the advance system.
Whats been done to it?
The pump isn't programed to the PCM in the same way as current vehicles. And the EPIC system can cope with up to 8 degrees of bolt up error, outside of those 8 degrees and the engine light will come on.
I know you've set the timing correctly with pins but allow me to suggest a couple of things to try
run the engine from a gallon can directly into the pump.....if it runs ok, you've an air ingress issue.
Slacken the 4 bolts on the pump pulley and move the pump round a fraction and see how it runs.
I've seen a few of these have pump body alignment issues where by the peg hole isn't in the correct position in relation to the pump housing.
Also.......the feed and return pipes are in the correct ports aren't they
