Ok, let's do these in order...

The Oakway SD60's have/had K3LA's or K3HA'a (both sound exactly the same, the difference is the manifold they are mounted on). This is the exact same type of horn that is still common as dirt on BNSF and UP. Until the GEVO's and SD70ACe's the K3LA and K3HA were the standard horn on both UP and BNSF, with all new units being delivered with them. On UP, most of the SD70M's have K3L/HA's and on BNSF most dash 9's and standard cab EMD's have K3L/HA's.

BC Rail's GE's had K5L's and K5H's. (Same thing as the K3A's, both sound the same, the difference is the manifold they are mounted on). The K5L/H differs from the common K5LA (Amtrak and most passenger units) in that the A stands for Americian tuning, where as the absence of the A means the horn is Canadian tuned.

The NP's standard horn was the P3, so old BN/NP GP9's wound have P3's on them. The P3 was also the standard horn of Southern Pacific.

This website:

[atsf.railfan.net]

Lists most of the horns that have been manufactured in North America, as well as having pictures and sound clips of each one. If you want to hear the difference between the three you mentioned this site is a good site to do that.

Matt
Horn collector in Moscow ID