Check out Macsales at OWC.
They have a format where you select your model and then it lists what's compatible with that model so there are no mistakes.
Their prices are VERY attractive too.
I recently got a 24 inch iMac Al, got 4G matched RAM from OWC, it arrived the day before my iMac did so it was sweet to up my RAM first and THEN power up for the first time.
Very satisfying.
You will also find very nice vids on the site that walk you through installation of the upgrades that you are buying from them....it's very nice and friendly for folks who want to get better acquainted with their machines and maybe not have to drive a bajillion miles to have hardware upgrades done at Applestore.
NO.
I do NOT own stock in OWC.
😀