Actually

from what I understand you can have two engines on the bridge at the same time. Examples are as follows.
(1) You can run two engines on the bridge together if they are separated by at least 5 freight cars. The key is to keep 2 engines off the same span of the bridge at the same time.
(2) I have seen doubleheading across the bridge with a K28 and a K36, or a K28 and a K37.
(3) Needless to say you could also doublehead 2 K36's, or probably 463 and another engine.
In a shot of my fathers from around 1960-61 there was a Kiwanis trip in the fall where a K28 and K36 in fact doubleheaded on the trestle.
Seems like there is a qualifications, or an exception to everything on the narrow gauge out there if you look hard enough.
Greg Scholl