It's not an easy task to find and get all the relevant technical datas for such a LCD upgrade job, as is the panel/inverter exchange job itself. - Especially if a notebook is not right out of the box specified for any higher res panels by the vendor.
In other words, for the X6x-series it's not like for an R50p model, which had been already specified by IBM for the higher UXGA/QXGA resolution panels and where IBM also offered therefor all the right LCD parts (the panel, inverter board, hinges mounting parts etc.) out of the box.
If you look over the FAQs from the links I showed above, you will see that ScreenTek, LCD4Less etc. always too do write...
Q: Can I upgrade the size or resolution of my laptop LCD screen?
A: Screen size cannot be upgraded. Your laptop resolution may be upgraded sometimes depending on the type of video card contained in your laptop and if there exists a compatible LCD screen of a higher resolution. We generally discourage against upgrading resolutions as it is not easy to determine a compatible LCD screen between resolutions.
...or...
Q: Are some laptop LCD screens compatible with other LCD screens?
A: Yes. Laptop LCD screens may be compatible with other laptop LCD screens. Moreover, laptop makers like Dell, HP Compaq, IBM, Toshiba and Sony may source more than one LCD screen (as distinguished by the LCD screen's part number) even from different brand LCD screen manufacturers to install in the same laptop model. There are many variables to take into consideration like various physical constraints, electronic signaling characteristics and power issues.
...that's also since they don't sell and have fitting inverters and mounting parts for the individual lcd panels related to all the specific notebook bezels from all the different notebook vendors.
In sum up, even it is theoretical possible to perform an lcd upgrade for specific notebook displays, it's always hard to do so in practice, if you don't have enough approved internal informations about the specific notebook. And the Thinkpad HMMs don't give you here enough of the needed internal engineering informations that you would usually need to perform such a job, if it is not already designated for the specific notebook (like for the above mentioned R50p example)!