are you sure that the logic board from the 17 inch imac g5 is not the same as the logic board from the 20 inch imac g5 as they have the same part number 820-1747-A. Here is a link to the logic board for a 17 inch:Apple iMac 17" G5 820-1747-A Logic Board 2.0GHz Tested Working | eBay

Here is a link to the logic board from a 20 inch imac g5:imac G5 20

They have the same part number.