All the nonsense aside...
The ASB airbox eliminator kit is overpriced. Cut out the part of the airbox that holds the filter down and find some inventive way to strap it down. May way of securing it cost about 8 dollars. You can do the breather reroute for about 15 dollars or 40 if if you wanna get a little bit fancy.
K&N filter $45
If you want to get the most out of the bike you'll still want to tweak the race map ecm, which means another 500 dollar cable and software from EBR, That is 805 dollars. That's hardly budget. Get a laptop cable and bluetooth module for $130 and tune yourself.
As far as I am aware the baker transmissions are direct drop in swaps, either 5 speed or 6 speed. They will cost you though, around $2600 for the 6.
Revperf 1170 kit for the xb9, $999.95
Crank case boring $265
Crank shaft lighten, inspect weld and true, about $450
Head machining including clearancing for high lift cams and oversized valves, plus upgraded springs and matching oversized titanium valves, and a set of off road use only cams, about $2000?
Raise the redline to 8,000 <free>
Probably about $150 on a larger oil cooler and fittings.
Bronze oil drive pump gear if it's an older xb. $100
The belt is the same as the 1125, right? He shouldn't need the chain conversion unless he's going to be putting more than 130hp to the ground. If you do it, it's about $1000 dollars to do it right I think.
$500-$1000 for a clutch that is appropriate to be reliable for that amount of power.
So you are looking at about 7000-8000 dollars plus lots of hours of your own time and labor to make something that would do 160mph.