Some of you might remember the T540p I got for free from work a couple of years back - after its mainboard died I rebuilt my older personal T540p with the the remaining good components and a donor W541 I bought on eBay.
I'm quite pleased with the result. Its revised specs are: i7 4930MX, Quadro K2100M, 32GB DDR3L RAM, AUO B156HAN01.2, an HP Blu-Ray drive and an Intel AX210 WIFI card.
The Thinkwiki or Thinkpad wiki are helpful for every aspect of the laptop
Reddit was also pretty helpful as well
It helps to look for compatible cpus for the model because they are sometimes dependent on a specific Motherboard but that is just somtimes helpful