Yes you can manually pull up the top. But to make it easier and you are not fighting the hydrolics, unbolt the push rods from the frame of the top. But with the top already down, you might not be able to gain access to them. If that is the case, lifting the top will be slow and difficult. Ask for a friends help. We have a 1969 Cadillac coupe deville, I have had those cylinders disconected for years now. I'm 43 and not in my prime, but ihve just enough strength to pull it up on my own. The biggest issue is the acward angle and the distance you need to reach to lift these big cars tops (there is a reason that they are all power opperated). Have rags ready just in case of fluid leakage. If the car was stored out of the elements and you see no visible rust, all of the joints should be ok. But soaking any of the joints that are accessable, would/could save you money in bent frame work. Hope this helps.

It could be possible that you sprung a leak in one of your convertible top hoses which run to the cylinders, the hoses get weak and brittle over the years.