Amp gauge shunt

Guys, on the use of a shunt in an ampmeter replacement application, what would you use for a meter? Would you use a standard 50 / 100 millivolt aftermarket meter mounted under the dash, or could the OEM meter in the dash be modified to work with the commercially available shunts?

I have always had a distaste for some of the engineering (or lack there of) in many GM cars and would hate to use such a shoddy design as using the wiring harness as the shunt resitance to measure current in a decent car.