Converting old amp to IEC power receptacle?

I have an older NAD 906 power amplifier that has an attached power cord. The built-in shelving which I want to put the system has a bunch of the previous owner's IEC cords already run behind the wall, etc. To use one of these, how difficult would it be to install an IEC receptacle in the NAD unit? I gather that since the original power cord was not grounded, that I should leave the ground tab of the IEC receptacle disconnected? Many thanks for any tips.
The difficulty is finding enough room behind where the cord enters the chassis.
Then getting at the opening, without having to take the unit electronics apart.

If you can use a 'nibbler' (A chassis clipping tool) you can nibble out the correct shape. I warn you using a nibbler tool is time consuming, painful (for your hand) and a bit messy.
The chassis punch for IEC is amazingly expensive (Several $100's IF you can find one.) And then usually it will not fit anyway without taking the entire chassis apart.

An alternative is to have the IEC external to the chassis.
I am suprised no one makes a little box you can bolt through so the IEC is just stuck on the back in the little box, with the screws holding the IEC into the box really extending all the way into the chassis to hold it all on.

One issue with that is the cords often are too close to an edge to make that work. So even a small box as a dangle from the very short cord end sticking out of the electronics to the small dangle with the IEC in it. Someone should design the two ways in a small strong box and market it here, and eBay. Perhaps with the IEC part included in the kits.

I have two ARC gear items I wish i could make IEC instead of attached.. But the difficulties have stopped me from trying.
Then a few CD changers..

Anotehr means of cutting the hole is using a Dremel tool. The issue with that is vibration possibly damaging the electronics. And isolating the interior from the debris the Dremel makes. Plus most Dremel tools are not very good at cutting metal in that way.. (I would drill the corners with a drill to form the outline, the use a Dremel carbide disc spinning to cut the straight parts out.)

For the IEC chassis plug. Furutech makes a really great one for not too much money. Solid thick blades and nice screw down for the wires which can take up to ten guage wires. (I used one for replacing a 20 amp IEC so i could use a 15 amp cord)
Here's an inline socket - you can attach it to the cord and not have to change the chassis. - shorten the cord for better performance.
I used a dremel to cut the hole when I installed an IEC in my Harman Kardon amp. A little bit of filing to clean it up and in it went. This amp also had a two conductor power cable so I left the ground unattached.
I also rewired the the AC cable from the IEC with higher gauge wire. Probably a two hour job.
Did it! I ordered one where they had the cutout template online, so I just used a drill bit and a Dremel I used a big vacuum cleaner to hopefully suck up the metal shavings as they were created. Then I blew the whole thing clean with compressed air. So, by the time the receptacle arrived in the UPS, it was all ready to go. There's still a length of thin 18-gauge wire inside the amp, but it's just between the power board and the IEC receptacle. There's no ground on my amp, so I just left the center plug of the IEC empty.
Way to go!
Replacing the 18 gauge inside the amp is way simpler than swapping out the receptacle. Might as well go all the way.
Foodchain11 please provide a link to the cutout template.
What Timrhu said +1. Get rid of that bottleneck with better wire. Replacing the fuses with HI-FI Tuning or Synergistic Research will make a difference too(if you haven't already).