Bukwheat's secret squirrel Mikuni VM20, VM22 flange mount carburetor intake for piston port E50 cylinders (kit or stock, The flange is wide so some fin hacking may be needed)
This is as simple as pie and will give you a Carburetor that IMO has the most tunability...
1st. Source a Honda ATC90 or ATC110 stock intake (Ebay or boneyard)
2nd. When you recieve the intake be sure that the stock ID suits your application (My ATC90 intake is 18mm at cylinder, 22mm at the carb). If needed grind out excess alloy to make ID larger. Also the inlet and outlet is circular so any square ported cylinders will have to be altered to match.
3rd. For this to work you utilize the intake opposite of the way in which the Kheihin was mounted to the Honda (upside down). The thick flange will be for your Mikuni, the thin for the cylinder side. Expand the mounting points on the intake to match up to your cylinder and the Mikuni (1/4" to 1/3". Easiest way is to map it out using a standard base gasket). Expanding the cylinder side is most difficult as the intake makes a low sharp curve that impedes the process (small tip grinding tool works best).
4th. Depending on your cylinder fins,the outer flange (cylinder portion) may need to have material removed in order to slide in. Check this before you go any further.
5th. Install a base gasket for the cylinder port (Since Mikunis have a rubber O-ring none is needed for the carb side).
6th. Bolt up intake to cylinder. You will run into trouble with the low bending intake. Some grinding of the inner joint (at the base) might be needed in order to tighten the bolt (a hex bolt is an easier fit).
7th. Whip out your awesome new Mikuni VM20 or VM22 and mount it up.
Photos are of my ported Korado/Swinger1 with the Mikuni set-up
pics to follow as soon as I get my act together...