Extra chips in PDP11/23 plus cpu board

[Douglas Taylor via cctalk]

There is a CPU board for sale on ebay, M8189, and it has the usual 3 
chips CPU, MMU, FPU.  However, there are 2 extra chips and I've never 
seen that before.

Anyone know what this is?
Ebay item 122867114663  - Vintage Mint Digital DEC M8189 CPU Module 
Board KDF11-B

Doug