Ive had lots of napco over the years and have never seen( or heard of) a spicer 24 being used on napco systems. Every napco ive owned prior to 1956 had drivers side front diff and rockwell tcase
both the spicer 23 and the rockwell have "mirror image" versions that change the drop to front axel on the other side. For example spicer 23's have passenger side drop... while 24's have drivers side drop ( I believe Ford used spicer 24's).
Rockwells on early napcos had drivers side drop while in the transition period (early 56) they used a passenger side front diff but used the mirror image version of the rockwell to provide a drop on that side (cant remember model numbers at present)
Not familiar with what equipment was used on Coleman conversions so could be similar... any pics?
