Vintage lenses and teleconverter. Vintage TC native to lens or adapt lens to modern TC?

I own a fair amount of vintage lenses.
Some of them I use on a crop body (a6000), with or without a focal reducer.
I also use them adapted to full frame (a7).
I love them on their native bodies, but here lies not the question…

Considering the multiple vintage mounts and the desire to get a better reach out of some of theses lenses (the longer ones), I was wondering if adapting the lens to a modern teleconverter, rather than hunting down vintage teleconverters would be a viable option.
I am not sure how it would behave optically (teleconverter directly mounted to the lens, then adapted to the body, vs lens adapted to modern teleconverter mounted to the body), and I do not seem to find any clear ressources online.

Has anyone any experience in this regard?