Best idea would be to mount the pump on a new baseplate with some adjustment for belt tension. Fit a new pulley to the original pump shaft and drive it direct with the belts. The history of the Pansy and the effort you lads have put in so far deserves a good job being done and not another lash up. From the pump pics it looks like a lorry power steering pump and the clear plastic pipe looks to be a bit nipped. Hinge the mounting plate nearest the drive end with the adjuster moving the plate up / down. You could probably use one off an old lathe / drilling machine motor mounting plate and use the original checker plate mount welded on the new plate. this would make it easier to get to and service.
mark , are you aware of Boats for Sale UK & Ireland - Findafishingboat.com ?
might be worth keeping an eye on the 'hydraulics' section under the classified tab thing.