There's nothing inherently wrong with the 01A. Granted, it's not as strong as an 01E, limited to 5-speeds, and your 1.8T will have the wrong ratios, but on the positive side: 01A is perfectly adequate if you're budget conscious and not doing a crazy build, not picky about SMF vs DMF, allows for more plentiful 228mm clutch options than 240mm, and ones with TDI-specific ratios are dirt cheap out of Europe, and you don't need to replace the starter motor, center driveshaft and rear diff (if your 1.8T already has a 3.889 ratio) and consequently the rear axles too.