The 8051 has the SDS1000 software programmed into it, so you need a specific SDS1000 8051.
Are you sure the 8051 is faulty? I fixed up my SDS1000 and the 8051 looked dead, but something else (actually a load of stuff) had failed and an 8051 interrupt pin was being held low. When I disconnected the device(s) holding it low, the 8051 started working normally.
I have a circuit somewhere - I'll look for it but don't hold your breath...
Steve