Alternative parts: Replacing 6526 with 8520 cia

I found it hard to find 6526 CIAs to replace the dead ones in my C64s.  Scouring the the Internet hoping for an alternate I found this Forum discussion about using an Amiga 8520 CIA instead and what was different between the two chips. As 8520 chips are abundant on AliExpress I thought I'd give it a crack.

For the most part they work pretty well. Ive found some weirdness with my Ultimate 64 cart where the auto run doesn’t work, but mounting and loading normally is fine.  I wonder if it’s the clock?

Overall they seem like a good substitute until someone builds a better one.