[SunRescue] Sun 4/300 and Graphics Tower

[rescue at sunhelp.org]

I have a Graphics Tower but without the sbus interface or cable.  
Until I find an interface, I've replaced the GT boards with a 4/300
and memory card (501-1563).  Booting the 4/300 in diag. mode, it 
seems one of the simms has an error on the 9U expansion board.  The
relevant output from the prom: 

<Probing for Main Memory>
<Found 0x00000020 MB of Main Memory>
Memory Walking Address/Data Bit Write-Write-Read Test
 error: address=0x00800000, expected=0x00000001,
observed=0x20000001.(looping)
  Physical address:  0x00800000.
  (3U expansion memory) Expansion board #1 SIMM in Error:   U0703 
  (9U expansion memory) SIMM in Error:   U1603 

I tried swapping out the one meg simm at U1603 with a known good
simm, but the problem persists.  So, I'm wondering if this is a
defective memory board, or would putting a 4/300 cpu and memory 
card in a GT cause this problem?  The GT seems to use the same case
as the 4/110.  Would this be a supported configuration?  Also, would
anyone happen to have a GT sbus interface and cable?  I think this 
would be part number 501-1693.

-Ken