4000Q getting 5000 Turbo. BTDT? / parts?

[BBBurban at aol.com]

Thanks to all that replied to the looking for a 20v head and S4 exhaust.  

    My friend was able to get not only a 4000 Quattro, but as a bonus a 
complete 5000 Turbo (the previous owner wants the 5000's wasted automatic 
transmission back after we are done for some reason).  The 5000 Turbo wiring 
harness is in very poor shape.  Does anyone have a good used harness they 
would be willing to part with or a good source for one?  Would appreciate any 
leads.

    As a side bar what can we expect to run into with this conversion??  ANY 
BTDT??  Parts we should buy?  Performance modifications that are recommended? 
 What is the best way to handle the ECU upgrade?  Thanks all....

Hank 90q20v