Mountain Lion on a 64-bit "Nocona" Xeon - possible?

[Goldfish64]

I have a HP workstation xw6200 fitted with dual Intel Xeon "Nocona" processors. They are 64-bit and can run Snow Leopard and Lion in 64-bit kernel mode. However, due to the age and lack of SSSE3, I have to use legacy/AMD kernels. Now with Mountain Lion or anything newer, no kernel is able to successfully boot the machine, possibly due to the lack of LAHF/SAHF and/or other instructions. Nocona supports SSE2, SSE3 and NX just fine.

 

Has there been any development of kernels that are capable of running such old hardware? The furthest I can possibly get is shortly after boot with a corecrypto invalid opcode panic using sinetek's 10.8.5 kernel. Other kernels simply hit an invalid opcode 9E (SAHF instruction) over and over.