I don't think you will have to fabricate the
bracket. I believe the GT Hawks tachometers are the same size and almost
every GT Hawk had a tachometer, brackets are in the thousands. The key
thing about the bracket is that there are insulators within the bracket
for the two leads that mount to the bracket.
You have a great find at a stand out price. How do you know it does not
work? To test the tach head use a 1.5V "D" size battery across the
terminals. That voltage will not "pin" the needle. Make sure that you
check which is the positive lead to the tach head. You don't want to pin
the needle the wrong way.
If it does not work, you are left with taking it apart. It is actually a
simple electrical device with an electromagnet that travels along a
curved iron core. Often you will find a miss alignment of the iron core
to the electromagnet which causes it to bind. Adjust a big screw holding
the iron core and it will free up the electromagnet.
I am presently repairing a 64 Lark Tachometer for a freind that has a
damaged face. It did not work at all and now does. I am in the process
of having a new face printed for 64 tach's.
Here is a before and after pictures of 1963 Lark tach I bought off Ebay a
few years ago that I took apart and repaired. It now resides in my 1963
Lark Convertible.
Allen