Sell it as is. The is no liability to a present day owner with the orignial power cord there. That woudl be on FEnder, right? IF you replace that cord, then there could be an issue of liability if an accident happens on down the line. I also disagree that he 3-way installation is as simple as described above. It isn't rocket science, but there is one really correct way to do and quite a few less correct ways.
AS for the value.....that grille cloth leads me to question the originality of the main aspects of the amp...trannies, speakers, board components, pots, etc. I quesiton everything on these vintage amps these days.....and Ihave seen some rip-off jobs within the last year that cost some folks some good money when they bought something that wasn't what it was purported to be.
So, if you are going to market this amp, the date codes and good pics are more supportive of a good sale price than is that grille cloth, imho.