What type of Agnus chip do I have?

[Matt_H]

Here's some of the confusion: ECS != 2MB Chip RAM in all cases. The first ECS Agnuses allowed you to address 1MB of Chip RAM, switch between NTSC and PAL in software, and use ECS video modes (Euro36, Super72, etc.). The ECS screenmodes only work if you also have a Super Denise and Kickstart 2. Have a look at p21 of the Amiga Release 2 Getting Started Manual. DLH has a scan.

So if you have 1MB of Chip RAM in your A500 now, you have a 1MB ECS Agnus and the appropriate motherboard modifications to address the motherboard and trapdoor RAM as a contiguous block of Chip RAM. This was a very common modification back in the day.

The MegaChip doesn't need to "pick out" its RAM. It uses your existing Chip RAM and has 1MB onboard to give you the full 2MB.

[Matt_H]

I'm pretty sure the design of the MegiChip is functionally identical to the MegaChip- RAM and all.

The 8MB limit only applies to the Zorro II memory space. Chip RAM resides elsewhere, so you're clear for 10MB total.