J Crew Hat
I checked the gauge for the yarn you want to use and it's 4.5 stitches per inch on size 8. The original pattern uses 114 stitches = 19inches. That means you'd need 85.5 stitches for the new yarn. I'd cast on 84 (I agree with Ingrid on keeping to a multiple of four for the ribbing) and increase 2 stitches in the first round of stockinette stich just like the pattern says. After that it's all measurement. If your worried about it being a little too stretchy on size 8 you could try a size 7 needle.
GOOD LUCK - It's a classic looking pattern!