I've always thought the '60 was much better looking than the '59 El Camino , your conversion is looking great so far ! The Impala side trim was only installed on El Caminos built in California .
I did the same conversion about five years ago and it really is pretty straight forward except for the length of the bed . You might also want to look at the rear bumper . Here's a link to mine , you can see the rear bumper differences .