I agree with powertool that they may not be a big job on a tractor or commercial vehicle as they are usually more easily accessable and are also big enough to use a decent hammer and drift or burning gear if need be!
I am also not that conversant with these vans but do know it is common practice and often cheaper to have someone replace the axle assembly on an exchange basis. People often advertise this service in the likes of Autotrader.
The reasons are, that unlike the bigger vehicles mentioned, which more often use needle rollers, smaller vans use bronze bushes which need to be reamed to size and also need more critical shimming for the correct lift. It is also a lot harder to work when you are grovelling under a wheelarch than an open area like the above vehicles. It is not unusual for the kingpins to seize in the axle beam, which would require a hefty press or burning gear for heat, plus you can't get a proper swing as it is more awkward on a smaller vehicle.
Your mechamic sounds genuine enough so either ask his opinion on the viability of exchange or see if you can find a local company in Autotrader and ask for an exchange price yourself.
I am fully conversant with this work, have all the tools, but still paid someone to do this once on a Transit because it was cheaper and quicker.