Untested on boards with external Radeon graphics adapter. If you have such board, proceed at your own risk and document if it does work.
The flash IC is located at the bottom center of the mainboard. Access to the flash chip is blocked by the magnesium frame, so you need to disassemble the entire laptop and remove the mainboard. The flash chip is referenced as U49 in the schematics and in the boardview.
To disassemble the laptop, follow the Hardware Maintenance Manual.
This method describes a way to install coreboot with vendor firmware still installed on the Lenovo Thinkpad X60. It is reported to also work in Thinkpad R60, with the only difference being the board target you build coreboot for.
Default configuration of coreboot doesn't feature any flash restrictions like the vendor firmware, therefore flashrom is able to flash any rom without problems.