Thanks for the tip on Pegasus. A great resource. I think they had every adapter fitting I could imagine and some I couldn't, EXCEPT the one I needed, but they did offer a work-around that may work, but it also presents another problem as the work-around fitting that has a 3/8-24 fitting is only available with a -3 AN fitting and I want to use -4AN. This gets me to the comments regarding flex line swelling.
From my drag racing background, most of the clutch/standard trans drag racers are using internal hydraulic throw-out bearings instead of slave cylinders which requires the use of a flex line and seldom experience line swelling. That being said, the flex line must be a line rated for hydraulic clutch operation, of a proper size for the anticipated pressure and compatible with the type of hydraulic fluid being used. McCleod Racing is a great source for both the hydraulic throw-out bearing and braided SS clutch flex lines. Also keep in mind that when using a slave cylinder linkage, the amount of pressure on the system is affected by the pressure plate rated pressure and the length of the throw-out bearing arm. Longer arm = more leverage = less linkage pressure required to operate.