To find out which kernel version is currently running:
As far as the kernel.h file, I have the same file with the same size in my /boot directory. I'm running 2.4.1, so it doesn't appear to do much of anything (but I'm booting off floppy as well, so I can't be positive on that).
You've just experienced the FUD involved with kernel upgrades via an RPM. Do you feel like you got raped and have no idea what's happened to your system? I did when I did a kernel upgrade that way. I had no idea what the "upgrade" did to my system. Now I only compile from source.
It's not difficult and it's a hell of alot less stressful than an rpm "upgrade". Plus you have the capability to really customize the kernel to your system, so you aren't running extra stuff that will slow down your system.
You should be able to reboot your system. Hopefully you made a boot floppy during your initial install just in case things do go wrong.
At least with a kernel compile you can (if you follow the dirctions carefully) boot from a choice of kernels, so if your new compile doesn't work, it's just a quick reboot and you can run your previous kernel until you get the new one worked out.