[rescue] DEC PDP-11/23 memory expansion

[Scott M]

I recently acquired a DEC PDP-11/23 in a VT103 chassis. 
(Terminal + computer in a single package). 
Nice computer, but a bit short on memory to run 2.11BSD Unix. 
This page: 
http://en.wikipedia.org/wiki/PDP-11
says: 
> PDP-11/23 - 2nd generation of LSI (F-11), early units only supported 
> 248 KB memory, but could be modified for 4 MB support. 
I cannot find details on this "modification" anywhere. 
Does it involve removing the CPU board (M8186 KDF11-A), and replacing it 
with another, or can the original be somehow modified for 22-bit operation? 
Also what 4 MB memory board is recommended? 
Thanks for your help. 
 
Scott M.