Hi Richard,
Thanks so much for your comment and suggestion. I didn't know that Stephen Fagin communicated with people via email. I will try to contact him and see what I can find out. I think the Bell film is the only film showing the limousine still on Elm Street after the assassination that the 6th floor museum hasn't posted on their website.
Having requested copyrighted material myself from 6th floor museum I can confirm Stephen does personally respond. I guess the buck stops with him. He also emailed me to request that I take it down when I posted it (the copyrighted material) here at this site. So maybe he's a lurker
The request form you fill in has a section to state the nature of your material usage. You might get lucky and he'll allow personal usage of the film, for research. But probably not posting or using it for Youtube/here, etc.