Messing with the tach? Pro's please help.
 

I am currently putting a LSX 427 in my silverado. The tach only goes to 6000 rpm on the factory cluster. Is there any way to change the tach signal to the dash? My plan is to narrow up the numbers on the tach and make it say 7 or 8 thousand in the same area. Can this be done and somehow adjust the tach signal until engine rpm lines up with the new location of my numbers?

Should I just buy a five inch tach?