I have the shocks unattached at the axle, I feel like I need to take the wheels/tires off to give me the room to drop a side car enough down. It’s really close to going in, but I’m still afraid it’s going to be too high in the rear with the difference in spring heights.You pretty much HAVE to remove the shocks to allow the rear axle to drop low enough to slip the springs in. You should be able to loosen and remove them at the axle with ease. And it's likely that you'll have to remove one end of the pan hard rod, also.
The pan hard rod is attached at 2 locations with nuts holding them on. Are BOTH nuts resisting your efforts to get them off? They are massive nuts on giant bolts/studs, there should be little chance of them stripping or breaking, certainly you should be able to break them loose with a 1/2" drive ratchet or breaker bar or even simply a 12" adjustable wrench. There's no need for them to be torqued massively, the rod barely pivots and applies very little unscrewing force. Keep trying the Liquid Wrench-type products.
"Progressive" springs have some of the gaps between the coils smaller than what most of the other coils of the spring have, usually just at one end. The gaps between the coils on normal springs are roughly all about the same distance.
As for the panhard bar....yeah, BOTH bolts are immovable objects at this point. I’ve tried long socket wrenches, impact gun, electric ratchet...those nuts are stuck. Under the car while it’s jacked up doesn’t allow for the best ergonomic position to wrench in these things. But it’s corrosion causing issues I’m sure. They’ll come loose at some point I’m sure.