Primary always use non synthetic. Straight up ATF Type F fluid is great, you can grab some B&M Trick Shift Non Synthetic oil on Amazon for about $7 a pop which is pretty good too.
Barnett, Baker, Primo all the clutch companies recommend ATF type F. Type F doesn't have the friction modifiers as the design was for pre 70's style transmissions
I took the above advice and my primary runs better than brand new. I didnt need to adjust the clutch at all. Just R&R the fluid and all problems were fixed. Honestly, my shifting felt like it was going through glue. Yes, it was brand new primary fluid. Same as Ive been using for the past few years. I highly recommend B&M Trick Shift. I got mine from O'Riellys Auto Parts for $10.
