Hi - for the hardware hack, which will also give you Wi-Fi ac & will work through OS updates, you need plural parts, which are most economically sourced separately via Ebay; a certain amount of soldering is required.
1: part 653-0014 = Broadcom BCM94360CD Wireless ac/Bluetooth 4/LE card. Around $30 via Ebay.
2: Adapter to fit above card [proprietory Apple interface] into a mini-PCIe slot, as found in your 2010 iMac for the existing wireless card - this adapter is often described as: "mini pcie adapter for BCM94360CD" and is now available, much improved, in a v3 hardware version. $10-ish via Ebay. Make sure you obtain v3 and that it comes with its cables.
3: Aerial adapter/extension to connect existing bluetooth aerial to BCM94360CD - this is tricky to source and is often described as: "U.FL male to U.FL female pigtail cable" you'll need one of around 2'/60cm. "U.FL" [connector type] may be called: "IPX" - you can pay as little as a couple of dollars [from China]: mine came as their part: OL-2198 from: onelinkmore.com
For full Wi-Fi function/performance you will want a third U.FL aerial - of around 18" - for the extra channel used by Wireless ac - these are easy to source.
On the 2009/2010 27" iMac, you need to provide D- and D+ signals/voltage from the wiring to the old bluetooth module [which you remove] to the adaptor card - the v3 model I sourced came with a plug-in cable for this, with the far end tinned and ready-to-solder.
Very good relevant images are available from a long macrumors forum thread [focused on the 2011 model iMac] in this post . . . I do not believe with a 2010 model 27" iMac that you need to provide the +3.3v power to the little pads provided for this purpose on the v3 board [to enable bluetooth function if you run off Wi-Fi from inside OSX]; but instructions are provided in the above thread if you sensibly want to take a belt-and-braces approach..