Converting a Chandalier Hard wire to an outlet
Judging by the photos and your explanation, it shouldn't be a complicated job but there are a few things to take into consideration:

Local code compliance in New Jersey and your county/city - something I'm not familiar with.

How well you can make wire connections yourself. I've seen many DIYers and &quot;electricians&quot; wire connections and they were varying levels of &quot;lucky nothing happened yet&quot; to &quot;lucky only this part burned when you called me&quot;.


If you're confident in your wire connections lasting for 50 years+, its basically installing an outlet with a plate that fits that 4-O box (my trade slang for what I assume is in the picture). It should be properly grounded to be up to national code, so you'll need to know how to check for that. The pipe may already be the ground for it.
I'd hire an electrician for something like this because you get their expert knowledge/skills and its probably a couple hours at the most. Could be less than an hour if you have all the infrastructure in place minus the outlet/plate. To save a few bucks, you could always install the fixture yourself since you just need to plug it in.
If you do do this, here are some options/ideas:
You could use plates like these (for example):

https://images.homedepot-static.com/productImages/e888bbe3-2fa2-40e3-8112-08feb4fa3864/svn/brown-leviton-electrical-outlets-receptacles-5059-64_1000.jpg
You need to identify which wire is the switch leg and connect that to the hot screw. The neutral would go on the neutral screw. If you have a solid ground path through the pipe, you could use the ground screw in the threaded hole in the box. Otherwise, you would need to run a ground wire back to the closest ground source to make it properly grounded.