Be careful using LDO regulators on a PCB designed for non-LDO regulators. The pinout is often different
I should have mentioned that's why I suggested the LM2931 and LP2950 - they're pin compatible. Except for the max current and desired caps, they're drop-in replacements.
If you're removing the on-board regulator and replacing it with an LDO, don't forget to include the diode drop (0.6V) along with the dropout voltage in your calculations.
-j