I remember searching on this issue for 46-48 cars and there were a couple interesting techniques. I can't recall what they were, so I apologize that I can't pass them along now. But just search "hood spring installation" or something close and you'll get some possible methods to try.
There was a thread on here about this a couple of weeks ago. I tried the "Search" function and couldn't find it for some reason (the "Search" function never seems to work for me). As I remember, you load the spring up with a bunch of large washers which spreads the coils out so the spring is long enough to install on the vehicle. The you carefully remove the washers one at a time.