Whizbang

i was searching around for information on this but i could find the right terms to get any information. Basically i have an 89 with a bad motor that was half converted to carb. Now, i have enough S4 stuff, including engine harness, to put this thing back to running condition but in S4 format.

Now what problems can i expect to come across when i try to get this all together? Im expecting there to be some weird S5-->S4 differences im not thinking of.