Took a long lunch, took apart my VS2K and made binary & hex images of *all* 
the PROMs on the boards...

LPWR/VS40X 4-Plane Color Opt. -- 27512 EPROM -- "LM8832/083E7"
Ethernet Board? 5016803-01        -- 27256 EPROM -- "23-352E6-00 ABOfy/w8841"

CPU Board has 4 EPROMs on it, by the memory array, as follows:

(Back edge of system board)
============================================
+---------------------------+----------------------------+
!   27512                 !   27512                  !
!   LM8838               !   LM8836              !
!   051E7                 !   053E7                 !
+---------------------------+----------------------------+
!   27512                 !   27512                  !
!   LM8835               !   LM8838              !
!   050E7                 !   052E7                 !
+---------------------------+-----------------------------+   

My system has a DataRAM add-on memory board (12Mb total I believe), and 
LM8836/053E7 (Upper right above) is removed and on a "flying daughter board"
attached into the original socket by a wire lead.  There are 2 other chips on 
this
board... 16-pin DIP IC's, possibly small PROMs?  

Anyways...  27512's are 64KB EPROM's, so this is 256KB of PROM.  I have no
clue just yet whether this is 256K x 8-bits, 128K x 16-bits, or even 64K x 
32-bits.
If its 32-bits wide, to modify the boot PROM monitor would obviously require 
all
4 PROMs to be reprogrammed and replaced.  

I'm sure I have enough '512s to fool around with, so I'll dig into it some 
more...

Any insight into this would be appreciated.

Pete