I tend to think you are stuck, jadebullet. Unless gumbytrain ever told anyone that he was releasing his work to the public domain, which is possible, but I have not heard about it. Clearly by placing undecorated models on the DLS and by taking the trouble to produce simple and easy to use mapping of his models, gumbytrain intended a lot of people to reskin his stuff. However his eula does not state that intent. I, like some other older members of the group got a blanket permission from him to reskin his RS3's, but unfortunately for me I didn't think to ask about his 44T at the time. It is too bad he didn't clarify his intent in the eula, but my sense is that if you don't have specific consent, you can't reskin and distribute.
Maybe it is time for some other public spirited creator to do a new version of the RS3 with a good cab and some of the various marker light options and release it for reskinning.