What I would do is,buy the stock coils and put them in and do the job once.Sell the other coils.I worked in a spring shop for 15yrs,there is a special quench oil that you must use to retemper spring steel then after that another heating process.Do yourself a favor buy new springs,sell the other ones.
Dave

If they are not heated and cooled evenly, you could have an uneven problem. But if you treat both springs the same, they will be even. The oil bath is needed if you are trying to make any time. In a shop it would be the way to go. But cooling them gradually will work.

However, I agree the easiest thing to do is just get another set.

If you cut the springs, go a half coil at a time check ride height,no more than a coil and a half, the more you cut the stiffer your ride will get, if you heat and set your springs the less spring travel you will have and may have trouble with coil bind, like a valve spring,do yourself a favor and call Vette Brakes Products and tell them what you got and what you want and get the correct springs, put the old springs in the swap meet pile