Acorn RiscPC 600 (OT - only 5 years old)

Sorry for the post about a machine too young for the list but it is the first of its kind in my collection. The chips seem to be from 1994 and the RiscOS (v3) splash screen also says 1994. This machine came to me as a box only having been an insurance write off because it jumped downstairs but there only seemms to superficial damage. It boots OK but the mouse which appears to be necessary in order to use the OS is missing and appears to have a proprietary connector. Can anyone tell me either if the mice are available? Alternatively is it possible either to persuade it to work with a serial mouse or to wire in a PS/2 socket in place of the original one so that I can use a PS/2 mouse? it seems to have 4M of RAM as 1 72 pin SIMM and 1 other memory board which looks like a miniature DIMM. It also has a HDD with 59 Mb used and 159Mb free so it must be about 220Mb altogether, this make windows look a bit bloated as there appear to be some apps there as well - it also seems to boot very fast compared with modern machines. Does anyone know what processor it has and how fast it is? Thanks Pete