Man! I read that title and thought...oh no! there not going to make it. Glad you got it under control, and cought it before the big bang! See you run at SEZS!
A stock tach should work on a Ford engine, but you need a 280Z tach. JTR suggests sticking the inners of a 280Z tach into the housing of a 240Z tach so everything fits, and looks stock.