Can't boot into Sierra after install of RX 560 card (help with kexts?)

I have a Sierra hackintosh that's been running fine for years. I boot from a Clover USB stick and then from the Clover boot menu, select the MacOS HD, and off to the races. All good. I had been using a Radeon 6000 series GPU.

Today I replaced the GPU with an MSI 560 RX (in anticipation of eventually installing Mojave).

Machine boots to Clover fine, but now Sierra won't boot. It shows the MacOS booting screen to about 3/4 of the progress bar - then some green dots appear on screen and it just freezes forever.

Since the GPU is the only thing I changed...what can I do? Do I need new kexts on the Clover USB stick? Change the plist? Or do I need to add kexts to the actual MacOS install? I am unclear whether MacOS needs the kexts on Clover or, once it starts booting, if it needs the kexts in the MacOS install HD itself?

Thanks for any advice!