Rob is right, the cut on the teeth is different from American Iron, and the 3.63 is radically different from the 4.10 and 4.30 judging from my spare 3.63 in the garage which is next to my spare 6-speed, lol. Bo London built mine and it makes very little noise (good install) with a slight whine at 50mph.
The gearing with the 6-speed and 3.63 is sweet. This combo makes 1-5th gearing a touch "tighter" than a 5-speed/4.30, and then you have 6th gear so you get to cruise at 80mph at 3600rpm. I got 24mpg running 85mph with a 400lb tire trailer yesterday. If you can't find the 3.63 then go with the 3.90, I would appreciate gearing a touch tighter than what I have currently, but that highway gear is sweet. At 250whp, you'll use all of the 3.63 considering I was seeing 145mph on the front stretch of TWS on Friday.
Don't think the 6-speed is "strong" though. People are still wearing-out and blowing up 4th gear; I see 330*f gear oil temps with only 250whp so I am careful. I've had good reliability though with about 20 track days on my trans, but I baby it, slow clutch engagement, and lift over bumps at HHR.