Preserving image class when combining images of same class

I have 2 images that are PseudoClass 256c with the same palette. 

optics 191 :/optics1/virtual_ant/etc/cl> identify secoora.west.qkm_sst.png
secoora.west.qkm_sst.png PNG 3740x7480 3740x7480+0+0 PseudoClass 256c 94kb

optics 192 :/optics1/virtual_ant/etc/cl> identify secoora.east.qkm_sst.png
secoora.east.qkm_sst.png PNG 3740x7480 3740x7480+0+0 PseudoClass 256c 
2.2e+02kb 0.350u 0:02

When I am putting them together:

optics 193 :/optics1/virtual_ant/etc/cl> convert secoora.west.qkm_sst.png 
secoora.east.qkm_sst.png +append secoora.full.qkm_sst.png

I end up with the proper image, but now DirectClass. 

optics 196 :/optics1/virtual_ant/etc/cl> identify secoora.full.qkm_sst.png
secoora.full.qkm_sst.png PNG 7480x7480 7480x7480+0+0 DirectClass 7.9e+02kb 
2.940u 0:04

I need to preserve the 256c palette they both have in common as the index 
numbers have meaning to me (not just the colors) Is this possible?

Thanks,
Brock