finding more than 8M memory on a 780 running 4.2

[RJ White]

We have a couple of 780's with 12M memory but it only finds 8M.  I changed
the 8M limit in locore.s to 12M where it looks to see how much memory there
is.  It found it ( real mem = 12.... ) but hung before coming up single user.
I assume I have to change something else.
I heard this was discussed once before in this newsgroup. Can anyone help?
thanx muchly in advance.
	-rj