Just came back from reffing a paintball event in the Netherlands, so I will get back to ye today/tomorrowmorning (Euro time)
*edit: I checked it out, put it in a pk3 file and.... it worked on solo multiplay.... so I guess your problem was/is the pk3 file. Sending you a mail now with link to the pk3 I made and which works
So it must work for you too. Oh and custom models only show up/are available when the server allows it and (in that case) only those who have the same model will see it.
Good luck, son of Arathorn......