That's awesome! I had access to an electron microscope at my last makespace and always wanted to decap a simple chip for reverse engineering. A close friend of mine did that with a SID and recreated it in verilog with good results, which I always found fascinating. Great work on the VIC20 side! And yeah, my VIC20 was never the most stable machine, crashing frequently but I also had a bunch of janky expansion boards attached so ymmv...

I'm also using the knowledge gained from reverse engineering the VIC chip to contribute to a soon to be released VIC chip replacement device called the PIVIC, powered internally by a Pico 2 chip.