Much of this already covered. But here goes:-
The four leaf springs for the 4 seaters are the same rate/stiffness as the springs for the 2 seaters so will ride the same, but the 4 seater springs just have more camber so they sit higher. Indeed there should be around 10mm clearance between the axle and the rebound rubber that is on the chassis unladen, depending on powertrain etc.
Leaf springs should be flat at laden ride height, that is how they are designed to be, as they then have maximum lateral stiffness, so reducing the need for a Panhard Rod.
Bump stops on the rear (& front) dampers are essential, the AVOs often come with no bump stops. Easy to add, either remove the top eye and slip them on or split you bump stop with a clean knife, coat cut surfaces with 'superglue' then push them over the damper rod and wrap them in that rubber self amalgamating tape. OK the loads through the damper bracket on the hub will increase and the early ones were not that robust. Check for cracks anyway.
To check for sagged leaf springs; jack under the exact middle of the front lower chassis cross tube to lift the front wheels just off the ground. Then without putting your weight on the car, reach through the parcel shelf opening and feel the gap below the axle and the rebound rubber. Should be the same both sides, one finger in is good, two or three fingers in that gap and the springs have sagged.
Cheers Peter (Director SSL)