Well John,
Yes, the PRR did do a lot of non-standard things (including paint their locomotives with green boilers...) to the extent that a lot of PRR fans refer to the Pennsylvania as the "Non-Standard Railroad of the World".
As far as majors that never operated narrow gauge lines, I would start that list with the Santa Fe (that is if you don't count that short period around the turn of the 19th century where the Santa Fe controlled the D&RG
.
Bill Daniels
LaLaLand
p.s....that's a nice T&NO T-class (31?) in today's picture of the day!