Modern systems require processor support in the BIOS and motherboard. To start I would find (and post) links to the Lenovo Hardware Maintenance Manual (HMM), which will list all of the processors supported by Lenovo in that system. Any of those would be "guaranteed" to work.
Further evidence of supported processors can be gathered from the BIOS. Find (and post) a link to the latest BIOS for the system. The reference notes and documentation for the BIOS will indicate what other systems that BIOS may be used in. After researching the motherboard part numbers and supported processors in those systems (via the HMMs for those systems) you should be able to create a more complete list of supported processors. For any systems using the same motherboard (same part number as in yours), any processors listed should be guaranteed to work. For those with different motherboards (using the same BIOS), any processors listed would probably work, but there could be design differences (e.g. power requirements) that might make some combinations a no-go.
Any processors not specifically supported for the system, motherboard, or BIOS might work but there would be a high risk for failure.
So here is the task at hand:
1.) List all processors optionally installed and/or supported in your system.
2.) Find any other systems using the same BIOS as in your system (if any), of those find out which ones use the same motherboard, and which ones use other motherboards (if any).
3.) List any additional processors supported in any other systems you find using the same motherboard (if any).
4.) List any additional processors supported in any other systems using the same BIOS but a different motherboard (if any).
At the end of step 3 you should have a list of processors "guaranteed" to work. Step 4 may turn up additional possibilities but success would not be insured. Anything beyond that would be a much bigger risk. Let me know what you find, Scott.