You use 'clrmamepro' utility to convert one mame rompack to another. It takes a while and is not very simple to use as there are so many options, and you must get the specific .DAT file associated with the mame version you need. It can convert a later rompack to any of these versions you guys cannot find.
Pretty sure it's not as simple as that....why then do they release rollback sets? Roms are removed as well as added over time. If the rom is not in a later version but was in a previous version then clrmamepro isn't going to materialise it out of thin air. I think (and I'm going to investigate it tomorrow) that once you have the latest Mame, the latest rollback set, the DAT file of the set you need and clrmamepro then you might be able to get sorted.
Also I can't seem to install XMame to my micro SD....right protected or something. Is ext2 still a requirement?