Thanks to all of you for your input. I see that most (actually none so far..) ready to go setups do not include the longer wires for the 3800 taillights so I will have to lengthen.

There is a $50 difference between the kit offered by Jim Carter and the one by Classic Parts although they sound exactly alike. Not sure why..

I've sent a request to Brillman to see if they can make a 48 harness.