Well, I didn't reply because I disagreed with this part, in bold:
Looking on eBay and online shops, I realize that there are no NTSC VIC-II chips to be found. So I entertained the thought of converting at least one of them to PAL. Besides, most of the cool games and demos are in PAL, right?
On the demo front I would totally agree, but not so much the games part. If there's a cool (new) game out there, 99% of the time it will have NTSC support. On top of that it'll likely play a touch faster and smoother, too.
If I ever feel the need to run a PAL machine I have an Ultimate64 for that. But that's it. And that's almost never the case. (I
like demos but I don't actively sit and watch them all the time, hence why I've never felt the need for a dedicated machine.)
In my experience, if you need a spare VIC-II chip it is going to come from a parts machine graveyard. There are literally
millions of NTSC C64s in existence. The problem is that in the last 4-5 years the prices have gone from $100 for a NOS boxed C64 to $100 for 2 freaking SID chips! It's totally nuts.
By the way... have you heard of the
VIC-II Kawari FPGA? It is a modern VIC-II replacement, has some new features and even offers pixel perfect HDMI output. And, it can provide output in NTSC or PAL. In fact, you can switch
on the fly if I remember correctly. It's still very much in development, I think, but you can learn more about it on this
great video by Adrian's Digital Basement. Super bad ass project. Unfortunately, global chip shortages blah blah
If you don't have an Ultimate64, I can certainly understand wanting at least one PAL machine around so you have every option available to you.