That is not a conversion, that is a car 180sx with a nissan silvia front end, aka a sileighty. If you mean you want to do a swap like that, the aerodynamics of the capri again sort of interfere with that. I have seen one with taurus lights fitted to it with MAJOR body modification to make it smoother. You'd have to do that, or modify an existing kit to make it fit properly.
This isn't something you can just approach and do in a weekend. I now have two cars with hidden headlights, and neither of which have any problem as long as you maintain the wiring and keep everything in decent shape. As far as major replacement it's fairly easy to get a new motor as it's shared with the probe.(note: the assembly is NOT shared, they do differ)