the only real difference in the two is the horsepower, the GTiR is a little stronger, about 20+ hp stronger. they both were built with AWD trannys thats why people are swapping them into FWD cars, typically they do not include the AWD transmission so its really nothing to worry about. you chose the wrong way to go by piecing it together, not is it expensive but its a task to find pieces. as for the harness its probably best to get an un cut harness from a 240sx with an SR20DET. check out
http://www.afterdark-tuning.com ive talken to him alot about this swap for my 98 sentra he says its a direct swap and he could perform it for less than 4000 including the installation, and it would start up without any other pieces other than what came with the package for 4000