Can I use a 21.5" iMac Video Card in a 27" Model?

As the GPU assemblies ( card + heat sink) are physically different for the 21.5 and the 27, there is no "drop-in"exchange. From eBay images:

The Terms of Use for this forum, do not allow us to post links for hardware repair guides or hardware upgrades.

What you need to do is Google iFixit iMac Repair guides and some third party vendors for a replacement GPU .

The fact that you don’t like the answer does not make it incorrect.

A 2009 iMac is not worth the cost of repairing it, even assuming you can find parts cheap online and do what work yourself.

You can easily find a complete, working 2009 iMac on eBay for under $100.

It is a waste of time and money to try and repair that old of an iMac.

The company that you work for, should replace it with something new or newer for you to use.

OK. Here’s the answer we can give you.

Google is your friend. You can find self repair oriented teardowns out there on the interwebtubes with a few clicks.

We can’t advise you when it comes to doing DYI repairs and parts sourced outside of official channels.

Good luck.