A bit of WD40 & a 7mm or 1/4" socket will get those clamps off, then a foot of hose from a motor factors for a few quid will see it sorted in no time. I think it's trying to tell you it doesn't like being stood!
What an awesome story! Congrats on getting the Ventora back in your ownership. I wish I could do the same with my Dad's old Mk3 Cortina he had when I was a kid, but sadly OVH 112P is long gone. Again, well done!