You don't need to do any chip ram mod to the Plus. The Rev. 8A motherboard comes with the 2MB Agnus, with 1MB chip on the motherboard and 1MB can be added through the trapdoor.
The only exception that I'm aware of is C= sold a few Plus's as "regular A500" models one Christmas, due to inventory issues. They'd stick a 1.3 ROM in there (sometimes also added for compatibility) and only half the RAM. Sometimes they'd also swap back to a standard Denise. So you might wind up with a "non Plus" model based on the case, but with an 8A board, and the ECS chipset, only with a 1.3 ROM... blah blah, Commodore was funny. Mix-n-match!
