It's been a few days but I actually have a 300 MHz upgrade in my 6400. I've made a video of it working and loading here:
I'm using a version that identifies as 1.3.7 on OS 8.6. Here's a link to that: http://archive.compgeke.com/Drivers/Mac/Maxpowr_G3_L2.zip
I'm using a version that identifies as 1.3.7 on OS 8.6. Here's a link to that: http://archive.compgeke.com/Drivers/Mac/Maxpowr_G3_L2.zip
