The forth (often optional) ROM you mention is a standard 2716 EPROM. You should be able to read it with your EPROM reader. You can also view it from the System 80 itself with an assembler. The address is from 12288 to 13823.
If it is a blue label model or the mk II business model then the ROM will be factory fitted. They have utilities in them which can be activated by going to an address. Details of what those utilities are can be found in the users manuals here.http://www.classic-computers.org.nz/sys ... tm#bundled
If it is a standard black label it could be a utility ROM like that mentioned herehttp://www.classic-computers.org.nz/sys ... ilityEPROM
As to the second question, yes you can use 2732 EPROM chips to replace the standard Mask ROMS BUT they are not directly compatible. A little bit of rewiring is required under the socket. You can read them with an adaptor but I wouldn't bother as a binary dump of the ROMS are in the System 80 zip file here.http://www.classic-computers.org.nz/sys ... lators.htm
although you would have to split the ROM file into it's 3 (or 4 parts). Or just contact me and I'll send you the three ROM binaries.