Get the basic and upgrade to the top, possible?

Hi all,

I am wondering if I get the basic iMac 21" 2011 (i5 2.5 1.199 us$) would be possible to upgrade only the cpu to the i7 and add a SSD as 2nd disk.

When you buy online at Apple.com the basic one is not possible to add anything, just more memory, but the next one (i5 2.7 1.499 us$) we can choose to upgrade to the i7 2.8 and add SSD as a 2nd hard disk.

For me they are all the same (the basic 21" and the second 21"), so I was planning to get the basic one and buy the i7 and SSD to add to it, but I am afraid that Apple made something that would stop any one to do that (like different motherboard / firmware / etc...)

If that is possible, where can I chech what kind of SSD and bracket (or support) i have to buy to fix it properly inside?

How about the i7, which will fit to the iMac ? what is the correct socket ?

Doing this, if I buy the iMac as I want (i7 2.8 / ssd + 1tb ) would cost 2.299,00. If I buy he basic one (1199) and a new cpu and a ssd at Amazon (287 + 400 = 687), the final iMac would cost 1886 + tax . Ignoring the tax, I would be saving around 400 us$ .

Worth all this to save 400 us$ ???

cheers