According to the PDF instrustions, I didn't need to modify my motherboard because I already had 1 meg of chip RAM (I think I made the modifications many many years ago, when I upgraded from 512k to 1 meg).
The PDF instructions say "Part number 318069-11 is for NTSC use and part number 318069-10 is for PAL operation."
My chip is 318069-19. Some info I read on The Big Book of Amiga Hardware said the Megachip allowed using a A3000 Agnus...
I got the Megachip from SoftHut, and they originally sent me a "MegIchip", without any jumper wires, and I only had 512k of chip RAM with it installed. They sent me the current MegAchip as a replacement, but the jumper wire was broken off and I had to solder it back on.
I just checked the MegIchip that they sent me, and it has a 318069-11 on it. Maybe I chould try that chip in the MegAchip?