I have successfully installed a 2010 Macbook Pro Logic board into a 2009 case/Screen and a 2009 MB Pro logic board into a 2010 Case/ Screen. I can't verify for the 2008 unibody aluminum model but I suspect no, because the battery assembly is different. Hope this helps. I don't know if this really answers your question. I don't use icloud but when I have switched harddrives between computers and tried to open apps I bought from the app store it will let me use it on the new computer as long as I authorize it with my Apple ID. I assume icloud works that same way.
To replace the airport ribbon you need to take the glass off the display. It's possible but very difficult. Your airport card is in the display clutch. Try bending the pin back and reinserting cable. You'll probably be able to get at least your wifi working but maybe not your bluetooth and isight. Other options buy a screen assembly on Ebay ..... I sell 13 inch ones but I found this one. http://www.ebay.com/sch/i.html?_nkw=15+i... Or buy a broken/water damaged Macbook Pro 15 inch for 300 or so dollars and take the screen.
If your keyboard works, but the keyboard backlight does not, most likely you need to reconnected the keyboard backlight ribbon. You may have knocked it loose while upgrading ram. Look to the logic board removal guides on here, the keyboard backlight connector is very delicate and has a flip up mechanism that you need to flip up before removing the ribbon. Then very carefully reinsert the ribbon. Insert it very far in. I usually use the back of a pair of tweezers/ or a spudger to get it way in there then flip back down the connector.
That little black plastic piece holds the wifi/ bluetooth/ isight cable in very tight, almost at an angle. For an example, on my current Macbook Pro 2010 I can get wifi but no bluetooth or isight because I haven't bothered with the cable. It has to be in PERFECT to get all three ( wifi/bluetooth and isight) Be very careful and reseat the cable, making sure not to bend any on those little gold wires. And then if you can't find something similar to that little black piece with adhesive on the back, tape is your friend. I can usually get mine to work by taping the back of the cable ( the cushioning part) to the fan with kaftan tape if you have it, electrical tape or even scotch tape. While you have the logic board out, clean it. With rubbing alcohol and toothbrush. You could get your whole computer keyboard and all back.
Be very careful removing + reinserting all cables. Especially display, bluetooth and camera. toothbrush + rubbing alcohol is the best process. First remove the fan and see if the water indicators have been turned orange.. I think that's where they are on this model. If they haven't take it to the Apple Store and don't mention water damage. They most likely will be though...
Do not take out the keyboard ribbon. Use a paper clip and connect 3 and 9. If you can't see the pins don't worry, they control the keyboard, so you are unlikely to damage anything. The computer will take a while to start up but you should see the fan spinning. There is another way if you google " jump start" or " Hot wire" MBP however this has never worked for me.... on a 2009 MBP...the video is for 2008 MBP but the pads are the same. I recommend trying to keyboard method first, because you are unlikey to damage anything.
Here are pictures of me starting my mid 2010 MacBook Pro from the logic board. http://db.tt/lXy8z3GJ. Please be careful. They are near the keyboard flex ribbon. If it doesn't work with the battery plugged in unplug battery connector and plug only Into AC power. My model has this problem because of water damage that seems to have affected the relationship between power button and battery. If at any point after starting up you can use your power button , perform an SMC reset. Hope this helps.