Hi Larry, As a rule, the gauge and its sender should be a matched pair with like electrical properties to get reasonable accuracy - ie: you can't expect to use a Stewart Warner gauge with a VDO sender. Of course, there are exceptions to this rule, but you have to know the electrical properties of the units to successfully 'break the rule'. (This assumes you're considering electrical gauges - not the mechanically driven ones.)

Beyond that, it's just a matter of finding a gauge you like (color, trim ring, etc) and getting a sender that fits the hole in your engine (right thread size). A sender that's smaller that your hole can be bushed, but one that's too big is useless.