[Rod]

I took apart an oldsmobile speedwarning like in your pic from a 73 OLDS 98 to see if I could use anything for a truck.. nope.... I did save the oldsmobile speedwarning buzzer though.

If swapping into a tach dash without speedwarning for example....
As for the swap ...of speedwarnings into another dash
your tach dash will not have a hole for the cable or the stud ... the stud being the lower arrow in your picture.

After I did mine differently I was told a small sockets around the stud and a little hit with a hammer will make that stud come loose.. you need that stud and the insulator fiber washer to be put into the tach dash. I didnt do it that way.. I just looked and played around with it till I figured it out.. I did it a few years ago,,, I cant even remember what I did but I remember that being about the hardest part to do.
The cable will need a hole drilled into the back of the the new dash rear metal plate... no big deal really.. I just used the same size drill as the hole that was in the original speedwarning dash. Used the original metal plate to help locate the hole.... the cable slips into a plastic cable holder in the speedwarning speedohead. Thats what makes the extra needle move. Used the original bezel to locate the hole for the cable in the bezel.