Jeff, 2 items regarding your speedo issue:
1) my speedometer became unusable some years ago, the indicator would bounce wildly back and forth, and started making noise. I inquired online with several repair shops, none would touch it, referring to pot metal frame warpage and cracking. I did send it to Bill's Speedometer Service - he offered a replacement Stewart-Warner speedo that he claimed was far more reliable. The cable end needed to change, which Bill did. It works fine, fits in the instrument panel, looks almost same as Waltham.
2) Ammeter change - did you fine the 2 #12-32 nuts for the ammeter connection? One id #10-32, easy to find. Need 2 nuts on each stem, so wire connection is tight to stud, but no strain is put on meter case from stud tension. I put mine in with one nut, and it sticks badly, have to bang on the face to free the pointer...