We all know the 1.4 was the 1.9 less a cylinder. Unless the three cranks are 120 degrees apart they will vibrate. That is why the special flywheels and balancer shafts were fitted by Audi To further smooth out the 90 the DMF was introduced. Now I for one can not say for sure that the 90 will operate smoothly or how long on a SMF. Later 4 pot diesels from Audi also have DMF so they must have proved it the way to go. PERHAPS a SMF fitted to a 90 that is then fully balanced by machining the flywheel may be the ultimate answer. But until then you are really in uncharted or long term unproven territory when it comes to fitting a SMF to a 90. But if people never tried to find a solution to A2 issues those issues could end the A2s in question.