The foam they do come with is valuable. If you have leftovers from previously used sets of tires, sell the new ones that come with your new tires. It should be easy to turn them over and it will take a bite out of the cost of your new tires.
If those black foams are the same hardness as the original 1/8 black foams they're WAY to firm for SCT's. The originals were too firm for 1/8th buggies which weigh 2x what a 2wd SCT does.