please copy and paste these three pics. I made them high resolution but they are automatically downgraded on this site. When repasting them in an other folder you´ll get them high res again...
I marked both holes of the Parts Place/Ames hood tach. As you´ve mentioned before there´s a threaded brass hole that´s meant for the (later style) vent tube and then there´s a second one near the brass hole. The PY hood tach is missing both holes completely. If you should use a rivet - as I did (it came with the hood tach) - or a third stud or if you´ll need the third fixation at all -- I think that´s your own decision. I felt better knowing there´s a third fastener...
Please note: the brass threaded hole is protected with some small black plastic pin so you will have to look for it on these pics of the lower side...
You´ll see both holes best from the inside view:
BTW - in the first picture you´ll see the complete unit including hood tach, harness, fuse and the above mentioned rivet -- the latter one in the left lower corner. In addition you´ll see the template that didn´t work for me...at least I wasn´t able to fix it on my hood the way that the tach would have appeared at the correct location. IMO it´s meant for a GTO hood.
You also will notice that it is easy to disassemble the Ames/Parts Place hood tach - there are only 4 special bolts that you will have to open - I did it with some small pliers -- was much easier and faster than masking the tach - especially because the small inner edge just in front of the glass should be kept black and not body color as shown in this last picture:
