Parallling caps will work, but if you wire them for the extra voltage you don't double the uf capacity. You don't get something for nothing. Being external you have lots of options.
Get this wire wound off the backwall and keep it off. The emitter resistors are not critical , nor in the signal path. Current sharing is not that difficult to bring off, but if upgrading go with metal film or metal oxide. No need to mess with the values or sizes of anything on the backwall, that was usually very reliable....