Sorry for the delay! I know it sounds crazy to some of you but as some other told. 1. Starting for the beauty of the machine, I decided remove external hard drives and even I had a raid lacie thunderbolt I wish I can also put inside both of them.
2. I should took the imac with a hdd instead the ssd since, I had to spent money looking for the exact parts and all the time researching but works! everything works like new, I'm writing right now from the imac.
3. For those interested the drive I choose is the new seagate which are the fastest spinning drives which mine run 200mbs faster than few ssd sata2 and about 130mbs reading. So i'm having "like" ssd speeds with a 3tb capacity and leave the system in the faster pcie ssd.
For those who are interested in the process I'll post the pictures later. Also I'll mention few issues I go over it during the process but nothing to worry.
I wanted to do it because aside of bring me experience since I do some repair for friends and relatives I practice in working on it. Don't worry soon ill got the apple certifications.
Thanks to all! keep in touch!