How to design a double v block ?

We are in need of a v block for our Design and fabrication project.
We want to hold work pieces of the range 20mm to 80mm.
How to design v block for the required dimension?
should it be heat treated after making?

Unless your project is designing of V blocks better buy a standard product that is freely available in the market. This will save time and money in the long run.
https://www.rentapen.com/2011/12/19/jig-or-weld-fixture-v-blocks/