[IdahoDoug]

I had the same experience with my 59k 1984 model regarding the vibration. Did full engine service and it ran fine but at idle it would vibrate the interior plastics. Off idle was fine but it was so annoying to be in a pristine low mile classic sports car that I felt like I had to make excuses for. So I replaced the motor mounts and that proved to be the issue. I used the $38 Meyles from Pelican with good results. I understand they may not be up to OEM standards, but $500 for a pair of pedestrian motor mounts from Porsche seemed crazy to me. It's not rocket science to make a set of molded rubber bits with threaded mounts and a metal bracket.

Someone asked an important question about the vibration. Does it continue at higher RPMs? For setting the balance shaft and timing belts, there is a guy on YouTube who's work was stellar. I cannot recall his name but on my thread about this within the last year, I specifically praised him and identified him as a great video choice. You might watch his video and decide if you got this down, or missed a detail or two. Just search on my name - others here recommended this guy.