I would go with the WBX modification to simple avoid all the unforeseen problems with converting...

I finally have tracked the high emissions at idle to the "new" VW idle control module was not functioning correctly.
I was able to pass tests with a 218 out of 220 max last test. but had to do a lot of adjusting each time to get it to pass.

And currently a leaking injector.  I did a pretest and the HC was 450.  The last test and the pretest was done with a new injector leaking and getting worse. It also caused idle problems.

I will have 4 new injectors (replaced under VW parts warranty) on Friday to put in :).

The exhaust was smelling good with a temp injector in.
THe five speed .457 SA gear box matches up well with the RPM band of the modified WBX...

You can build the WBX to the power level you want...

http://shoptalkforums.com/bbs/cgi-bin/forumdisplay.cgi?action=topics&number=37&SUBMIT=Go

Has a lot of articles about the WBX and what you can do with it...

Robert