Mopar Action,last issue,did an article on a 65 Coronet,white, w/a 5.7. That was built by a friend of mine before he sold it to the gentleman in IL.I don't know all the details,what I do know:
Yes it needed trans tunnel/crossmember mods(rfe),
yes,it had throttle by wire and cruise functional,it has an 8 3/4,I don't know about vss signal,
yes the speedo worked. He worked closely with Street and Performance on these issues,so they should know the work arounds to make them happen.
I know these issues;TBW,CC/spedo were his biggest issues,but it can be done!
He sold it and built another 65,this time w/an Alter-K and a 6.1 and all this stuff is functional again. Street and Performance may be your best resource.