With the shape of the 71-7 dash, the way it curves (if you have the rallye dash with the round gauges anyway) there's no way to install an aftermarket DIN deck and not have it look like ass. However if you have a standard dash with the long bar speedo, the radio mounting area on those is flat so it can be reasonably done.

I mounted mine under the dash because I despise the cut look. They make generic under dash radio mounts.