Kuno,
Let me know if you need any other dimensions for the hinges. Just describe what you need OR circle it on one of my photos and I will be more than happy to go out in my shop and measure it. They should be fairly easy to fabricate once you find a way to jig the bolt "tubes" in the arms so that those mounting tubes are all parallel with one another, otherwise the arms will bind.
(Helpful Hint: When welding the bolt "tubes" to the top and bottom of the arms, drill holes in a piece of angle iron the correct distance apart, then actually bolt those bolt "tubes" to the angle iron, then weld as much of the long piece of the arm into place while it's still on the jig, then unbolt everything from the angle iron jig. If you do it carefully it will keep everything in good alignment while welding, and it's no harder to implement than just having to drill two holes in a piece of angle iron.)
Regarding the pump, here in the States, the one that I've found that's virtually perfect for lifting the top is a pump from a convertible Chevy Camaro in the year range of about '93 to '02. It is strong enough, inexpensive, available, and comes with a check valve AND an emergency escape vale built right in. On any given day there are about a half dozen on Ebay.
I just checked Ebay UK and it seems like the Camaro pumps will be hard to find, but there were some very nice/appropriate-looking pumps from convertible Saabs and VWs that I noticed. The pump doesn't need to be terribly strong, but it needs to have power up AND, optimally, power down (instead of just "gravity down"), and it is good to have a check valve to hold it half way up, and it is optimal to have an emergency relief valve. Well, fortunately for us, those are pretty much the exact parameters that a pump needs to have for use in a modern convertible of almost any make. Alternatively, you could definitely find something from an industrial supplier, but it will be much more costly and complicated. (I've tried that route. It's confusing and difficult.) The major car companies have already solved this problem for us, unknowingly, with their products for convertibles. Cruise Ebay for a while and you should be able to find something good.
Here is a picture of the Camaro pump that I like. When shopping, I would stick with a pump from a later model car. There are lots of good pumps from '60s and '70s cars, but I've found that they are less likely to have all the cool check valves, etc. built in.
