Most popular tach in the 70's and other stuff

Ok, you guys older than me(44), step up:

Back in the mid-late '70's, what was the most common, popular tach you would see in cars?

What did you see more often..am/fm converters or underdash 8-track players?

Also, if you had to pick ONE vintage sticker from that time period to have, what would it be?

I wanted to add a couple period-correct accessories to my '73 Sport, but it must look authentic and not the "I bought something new that's supposed to look retro" crap.

Thanks.