Welcome to the world of 200Bs
137kw is a pretty big ask out of a street L20B (at the wheels that is), any particular reason you want that figure? Realistically you'd be better off going turbo if you're chasing that kind of power. Different options are listed around this website. Otherwise a set of twin sidedraught carbies will be your best carbie option for power.
Manual conversion is pretty simple, I worked it out and did it on a 200B when I was sixteen so it's definately doable if you've got the will and can source all of the required parts. You'll need to modify the gearbox crossmember but everything else can be done with basic tools.
Get some pictures up of your car, and enjoy!
_________________
green200b - aka Alistair
The fleet:
Australia:
'80 200B GX - the
green200b - hibernating
'81 RX-7 - 12A extend port - daily
'74 RX-2 - 13B bridgeport - cruiser
Europe:
'93 200SX - CA18DET - tourer
Green200B has forgotten more about 200Bs than we will ever know.