As stated by the first response, if all this is just so you can upgrade the CPU, I'd just upgrade to a third-gen (Ivy Bridge) i5. They're about $50 on eBay. There isn't much performance difference (clock for clock and core for core) between the 2nd/3rd gen and 8th gen Intel CPUs. Maybe 15%-20%. The only compelling reasons to upgrade from Sandy Bridge (ix-2xxx) are to reduce power consumption, for better integrated graphics, and new features like Thunderbolt support. (Ivy Bridge is just a die shrink of Sandy Bridge.)
Frankly, Sandy Bridge had the most important feature upgrade in the last decade (USB 3.0, SATA 3.0 support, low power consumption on idle). Everything else has been marginal or incremental, or can be added via a PCIe card (you bought a desktop so you could add cards, right?), or an annoyance (DDR4 RAM when all your old RAM is DDR3). The lack of compelling reasons to upgrade has meant that Intel has been trying to manufacture reasons. Like conspiring with Hollywood to require a new hardware-based encryption scheme for streaming 4k videos, thus requiring a Kaby Lake processor. Fortunately you can do that with a Nvidia 10x0 GPU as well now (AMD support supposedly coming later this year), to bring that capability to older CPUs.