Yes, get the water to where the water temp in your car is and measure the protrusion. I don't have the specs handy re the extension for a 71 GTV. What you're shooting for on extension is a .019" gap between the gap-setting screw and the pump arm when fully hot. You can adjust some at the screw that the TA plunger bears on. Some TAs will be shorter, needing the screw to be adjusted longer, and some TA will be longer, requiring the screw to be adjusted shorter. In many cases, more recent TAs extend a ton, and you can't get any gap, even with the screw under the TA fully adjusted in. In that case, you can shim the TA up some where it screws into the pump body with a spark plug gasket or other similar distance piece.
The blueish color is probably the remains of RTV sealer. The stock method of sealing thee is a round o-ring the crushes to a triangular cross section after some years.
My wife doesn't care. I clean the pot afterward, and do most of the cooking anyway. She was cooking dinner while I was doing this. She thinks my obsession with TAs is humorous.
Andrew