Replace pwr cord w/IEC socket on vintage gear?

You don't need to put an IEC inlet on the amp. You can just remove the existing cord and replace it with a new power cord. It will make experimenting with different power cords more difficult, but it will require no drilling or cutting out holes in the chasis.

I agree with Elizabeth.
You might even increase the value if done right.

I got the amp for $219, it's a keeper regardless, so I'm not concerned about loss of market value. The question would be different for an all-original 1961 McIntosh MC275.

With something like a Mac, I could see replacing the power cord by hardwiring as Onhwy61 suggested. That operation would be reversible. In my situation I don't know if I'll settle on PS Audio, Zu, Shuyata, Monarchy Audio, or Pangea. When I picked a cable for my Onkyo integrated amp, I went through every audiophile power cord in the house until I settled on the PS Audio Prelude. Later when I recabled everything with Zu, I replaced the PS Audio with the matching Zu, and voila! Instant synergy.

So for my purposes the IEC socket is a must.

Here's something else to think about: There are a lot of classic power amps from the '80s, with captive power cords--Electron Kinetics Eagle, Sumo, Precision Fidelity, VSP Labs, PS Audio, Amber, and so on. As good as these amps can still sound, I'm dying to find out how much they may improve with an aftermarket cord. After all, if it improves the sound of a Parasound, or Levinson, why not a Heathkit or Sumo?

Go for the IEC jack. I had one installed on my cj PV 12L. Cost was minimal and being able to experiment with power cords yielded fine results. Cost effective and fun!