I think somethings wrong here! LOL

AMIGO...You are NOT STUPID!!! first off you attempted and completed repairs that were clearly outside your skill set then & your comfort zone.....and admirable Attribute! You followed instructions ( which most mechanics have to learn to do after the do it their way first....= experience) and the only component I see that you lacked was the experience to know/diagnose WHAT wasn't right. If this life has taught me anything it has taught me this.....LEARNING IS EXPENSIVE....you pay for what you learn....everything you learn and anytime you learn, sometimes it is less expensive, most times it is more expensive.....but it is NEVER NEVER NEVER FREE OR CHEAP!
I think you did OK!!! and now you know at least ONE place to look if you feel unwanted vibrations.......all it cost you was a rebuild on your 904...... I know this much for certain.....YOU will never ever forget that learning experience.....

keep it up, some learn by books other by watching and others by doing any way you slice it it aint cheap....took courage to attempt repairs at that level, and you got a few years of driving fun....I think you did OK and it was a fun story to read
66Cuda