I did it ages ago for all my Captain Sim aircraft, but during an update, or a full uninstall/reinstall, I lost them all. I assume I deleted the folder with them still in it. I've never bothered to do it again because FSC isn't (or didn't used to be) very accurate with that info. I got some of the info from the Boeing 707 Wikipedia page, while the rest was from the aircraft.cfg (empty weight, maximum weight, etc.). :(