Not difficult, just takes time. Remove the old gauges, position the new ones and make some brackets. As for high beam and turn signals, we usually install them in the gauge itself. Its custom, and costs a bit more, but looks great.
While an earlier truck, similar concept. We mounted our gauges to the rear of the panel:



Here is another, a cougar, similar concept:



This is a 70 chevelle:



Its much more cost effective to use a new product and install from there, rather than putting new "guts" in and refacing the stock gauges.

A great alternative to Autometer is the Faria Performance line. We have been working with them for a couple of months to bring these to market. 100% made in the USA and about $369 for a 6 gauge set with electronic speedo.