Welcome! Would love to see pics of the cars! Swapping a 13B from the S5 isn't a terrible job. Keeping the fuel injection requires some work. I went with an 84-85 13B swap on my 85 GS. Everything was plug and play and bolt on. Super simple. However, a friend of mine did the S5 13B swap on his 85 and kept the stock injection. His username here is schreindogg. Shoot him a pm if you have any questions.

 

Hi and welcome, looking forward to seeing your build.