Mine is 1" away using the stock 2863216 440 18" fan blade with a 3462179 clutch (which is supposed to be from a 400 Max cool application)
This is with a 3 core "055" radiator

When I was running the MP Viscous package the clearance was about 1/2 - 3/4"

I have heard some use a clutch made for a Jaguar which is shorter...