@wlp3 I might suggest you get a really good drill bit and power through the steel and find a grommet that will capture the cable of your choice. Forget an IEC--worthless additional connection in this case and would be a pain in the rear cutting through all that steel. Go with the cable you desire and size accordingly.
I might suggest Supra Lorad would be a good choice. Go for the heavier gauged one. Flexible, easy to work with.
Also, agree with replacing those caps
Lots has changed over the past 30 years, especially civility. Very sad but there are still those out their willing to give a hand. Good luck.
PS-built a Hafler pre/power amp years ago. Good memories.