If the local Autozone doesn't rent it, my friends either make it or pool money togerther to buy it.

I changed the rear springs in my mercedes because the original springs were sagging. The new springs cause the car to sit 2-3 inches too high in the back. Sitting too high in the back causes significant driveline vibration over 40mph, and my car has a driveshaft that is unique to only 280slc and early 380slc. inns for sale in usa Also the driveshaft isn't easily servicable, I've found 2 companies online that can change the U-joint and balance them. I guess there are a couple of different heights of springs and the replacements I got were for the V8 models with the larger/heavier differential and driveshaft. I had to rent the plate style spring compressor for 30$ to replace the rear springs. Now I'm either faced with renting the same tool again to put the old springs back in or paying the 200$ to buy the tool. Buying the tool isn't really a money loser because I could always sell it for 150$ locally as the tool is rather inns for sale in usa rare and you have to use the correct tool on the mercedes because the springs are heavy duty. If I buy the tool I can take my time figuring out the best suspension setup. Also having the tool would allow me to change some other suspension bits. The only reason inns for sale in usa I'm hesitant to buy the spring compressor is I hate having he 200$ tied up in a tool when I need to do other important repairs like the 30year old fuel lines that are starting to worry me.
If the local Autozone doesn't rent it, my friends either make it or pool money togerther to buy it. So far, we bought a cam bearing install tool and a cam degreeing kit because no one rents them around here.
Marque board friends can often help. Most of the stuff I need, I can usually find another VW or Alfa guy who has one or can borrow it from the shop he works at. I'm actually thinking of starting to look at estate or business auctions for some of these things, so that I can join the helpers , but I've found most helpers don't mind moochers like me at all (..Don, lemme borrow that liner retainer set, and I'll buy you a 6-pack! ).
Buy it. It isn't that expensive and you can play with stuff when time works for you. On top of that you will almost certainly run into someone that will need the same tool and you can lend it to them. With enough friends buying and sharing tools you will always be able to fix something on the cheap, only buying when the network doesn't have one.
Last I knew there isn't a time frame on when you have to return one of the rental specialty tools, but it depends on where you go I guess. I'd double check with the parts store and see if there is a time limit. If there isn't one, then I'd rent it permanently for $30
I bought the plate spring inns for sale in usa compressor, I have to get the benz back on the road. I notice people not paying attention and a mercedes driven at speed has a special gift for parting traffic. This will give me the time to work out a set of proper springs, I'd like to see the car an inch or so lower but I'll have to see what happens. I guess cutting springs is universally frowned upon so finding the correct springs is my next task.
I don't know if the differential is sprung or unsprung, but changing the rear springs definitely changed the rear ride height. The car has an independent rear suspension so that might make difference in whether the rear axle is sprung/unsprung, but I don't really know.
If you have an IRS, The differential inns for sale in usa should be bolted to the car, its the most common setup. That said, its pretty easy to follow the half shafts and see. The extra spring height might be causing the shafts to pull on the diff, and then you can get some odd vibrations from the diff. On the e28 bmw, you get shimmies when the rear diff/body bushing is shot. So I might check those diff/body inns for sale in usa bushings and see if that helps.
As for cutting the springs, I don't see anything wrong with it. Just don't use a torch. Spring steel + plus random annealing isn't a great idea. I haven't cut springs before, but it would seem that as long as the remain surface can be seated, you just have a shorter spring. The rate will increase though, so keep that in mind.