On the front you only need to replace the hubs. On the rear, the best way to do this is to replace the entire axle. THe axle housings are different lengths between bolt-on and wire wheel setups, so switching hubs / axles won't work. You can buy adaptors which bolt a splined hub onto your existing hubs and put the wire wheels on those, but keep in mind this increases your wheel track by nearly an inch, if memory serves.
Another route is to buy bolt-on wire wheels. They are true wire wheels but have a flange behind them to bolt onto your existing hubs. Most people won't know the difference but anyone who knows these cars will spot it a mile away.
If you swap rear axles but retain your differential assembly, remember you need to swap the spider gears in your unit with the ones from a wire wheel unit. The splines on the wire wheel axle shafts and those on the bolt-on ones are different.