I did a few of these recently. 3 in fact: 2x T500 and 1x T400. SPI flash upgraded to 16MB Winbond W25Q128FVSIG + quad-core mod (wire in 2nd pic is prep for that). Core 2 Quad QX9300 on each machine.
I don't sell T500/T400 anymore, but people still send them for me to work on.
I offer a send-in service on my website, to do coreboot installations, but I also do other upgrades such as the flash and CPU upgrades.
The service is here: