moarh, in regard to your Redhat version, Redhat 8 does detect automatically for SMP. Redhat started doing this since Redhat 7, and starting from kernels 2.4.19 the SMP became a default selection in the kernel, because even if you don't have SMP, the kernel will not be affected by enabling SMP even if you don't have.
But, the question is why are you concluding you don't have the SMP support enabled? what are you basing this on?, I could almost bet that you do have SMP support enabled.
In regard to the kernel. The kernel that you will download and compile is not an RPM kernel, it is the vanilla source code of the kernel from www.kernel.org,
The only way for you to use the RPM of the kernel is if you upgrade your kernel via up2date with Redhat. Otherwise you will have to download the kernel, uncompress it, configure it, compile it, and then boot it.
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