You will need a V8 Tacho and the Temp gauge. You can modify the rear of the panel to adopt the V8 for the tacho, I think you add 1 resistor and move one. It's on the forum somewhere I think do a search.
You'll need a lot more than that! You also need the V8 front cross-member etc. ... Do a search - this has been covered before. The verdict by those that have done it - sell the V6 & buy a V8.
At the very least - canabilise a wreck with a V8 - you will have all the parts you need.