[Roadsters] speedo and tach early 67

[oliver]

what's involved in switching out the existing speedo and tach to an 
aftermarket replacement unit?

the new ones are all electric, right?  so there has to be some kind of 
converter?

thanks!

btw i am already in the process of installing aftermarket gages for 
everything else.  i had thought i would retain the speedo and tach but now 
i'm exploring the possibility of replacing those too.