Here is a link to the motor vehicle title manual.
https://ftp.txdmv.gov/pub/txdot-info...l_book_451.pdf
Of particular note to cobra owners is chapter 25. You are not trying to register a homemade vehicle as described in 25.13 you are trying to register a replica as described in 25.14 It seems to me that the homemade paragraph is causing the problem...
Finding a competent clerk that can understand the difference between replica and homemade.
I think having a copy of the manual with you and all relevant papers (MCO if built new, photos of your car as well as photos of original shelby proving replica status etc.)