but if you don't want to re-wire the car, I'd hit the junkyards. This would also give you the opportunity to score a box you could have some relays in for various things, headlights, main ignition, etc
"the new style"? I don't think there is any such standard. People have adapted fuse/relay boxes from newer cars to our A's. I did, but only under-hood, using the factory under-dash one.
In my '64 Valiant I replaced the old style box with new fuses for the existing circuits and added about the same amount of new ones. Since I relocated it from the driver's side to the passenger's side, I had to untie and reroute many wires. It's not an easy job, but it is doable.