I love what you are trying to do here, and I get it.
I might use this opportunity to sit down with your dad and take it as a real time to bond. If you've got some money and are looking to put a nice system together for him that really touches his heart, then I would think that you may want to actually spend time sitting down with him and maybe going through some nice options that are within budget and meet exactly the needs he has today.
This can still be a very retro setup, but perhaps that's completely wrong to the life he is living here, 30 years later.
My dad certainly has some nice older Acoustic Research (AR) speakers from years ago, but the smaller bookshelf speakers and in-walls that he uses inside the home are much more in line with his current lifestyle. He still uses the ARs, but they are in the garage. When his McIntosh tub amplifier finally gave up the ghost, he admitted that he couldn't hear any difference between a Sony receiver and the McIntosh amp. He doesn't have the ears, or the listening space, to know the difference anymore.
People change, and the experience of you spending that time with him to recreate what you can, but in an updated format will be a gift he truly will cherish.
That said, CD changers (or DVD changers), are all over eBay for not a ton of cash. Sony and Pioneer made them. They make sense if he carefully catalogs the way he loads them all. It is no easy task. Nothing at all like using a Bluesound Node audio streaming device and a smart phone.