The problem with hidden antenna's is when installed under a steel dash board it impedes the reception. Steel is the ground plane.
The reproduction solid mast made by Counterpart looks exactly like the original. Have yet to install but expect no problems. Got it from Classic parts for under $40.
https://www.classicparts.com/1967-72...ctinfo/69-961/
They have the telescoping version for $10 more, from what I understand the telescoping version was for AM. Will use the reproduction vs patching together another antenna from stock parts I have in hand.