They are a bosch shwimmer pump I think from memory.
they are not that big, if it was the external pump which I think maybe the VS Series 2 calais supercharged had, I think all VT's were in tank. I would say you could use the external pump, as a helper. But why? the Bosch pumps are cheap enough and strong enough brand new.
I don't like 2nd hand pumps as the wear is there meaning they can go anytime. Add to that most fuel pumps don't go as well after 100,000k's and can loose pumping pressure.