Overheating 360 new engine

Just a reminder, the 8 fin A/C water pump is under drove at about 0.90:1

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.

If you scored one with the fin backing disc, a little better yet.
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Are your sure about that? I thought the A/C cars generally had 6 blade pumps, but were over driven to increase coolant flow (and fan speed).