how to recognize earlier upgrades
 

I am going to dive into the suspension of my 1976 912e which has had quite a few upgrades - and not sure what is currently in there. How do I find out what torsion bar sizes are with them still in the car? Do they have to be completly removed to be measured? What is the coding to determine what they are?

This could be a long process to remove everything and replace what has worn out - 166k, and then have a strong baseline for the future.

You will have to take the t-bars out to measure the thickness of the bar between the splines. I would do the fronts and see if they are stock size. They are much easier to do than the rears. I wouldn't do the rears unless you plan to put in new ones.

Get yourself a micrometer and check the thickness. your fronts should be the same as the 911 and be 18.8mm I believe.