Bonjour Claude,
The simple harness can be crafted easily from a factory harness from a junk yard. The computer can be configured for the manual transmission without much difficulty. I have included 2 links for you to view a Buick with similar modifications. I can assist you with sourcing parts and computer tuning.

http://www.lesabret.com/ https://www.youtube.com/watch?v=FaKNPjPU4fE