I think someone said that the March Pulley system you are running is at about 0.90:1 so OK for 8 fin. But if you had a 6 fin it might not move enough coolant.
Edited to remove wrong Info. I got them backwards. But in almost all the AC and non AC "A" engines I took apart they all has 6 vain pumps, Even the date coded 1978 pump on my non AC 78 LRT.
