Converting a Stag tach to function with a V6

[ArthurK101@aol.com]

Folks, need a little help here.  I have a '73 Triumph Stag.  The engine HAD 
been converted to a Ford Mustang V6 (2.8L).  I know, I know.

I have the original Smith's tachometer.  It is for a V8 engine (says so right 
on the face).  I want to convert it to function with the V6.  Anyone know how 
I can do it or where I can get it done.  Thanks.

Art Kelly '64 TR4 (original owner), '73 Stag (new acquisition)