Rear axle drop when car lifted.

[dontlifttoshift]

OP, it seems you have two concerns.

1. The rear end hanging from the extended shocks. Like Marolf said, non issue. The shocks are perfectly capable of supporting the weight and there are hundreds of OEM applications where the shock runs out of travel in extension before the spring or suspension does.

2. The spring unloading from the seat. This is common as well, see above posts.

I have no idea what state of build your car is in but I assure you, weight has everything to do with it. If you are missing glass, upholstery, fuel, etc you will not have enough weight to load the spring properly at ride height. When all of that weight is added, you will need to adjust the spanner nut to preload the spring to get ride height back. At that point, you may find that you don't have a problem at all.