Ah, I think the light is beginning to shine through for me.
So basically, my GT Outpost almost surely uses a threadless steerer, but my Raleigh SC30 is some kind of anachronism in that it uses a threaded steerer.
So, if I ever want to change out the RST 781-CL suspension fork I will have to also change to a threadless headset?
I'll try to take off the forks of the GT Outpost and measure them, but having never removed forks before, it might take awhile. I'm sure it's an 1 1/8", as I have an older GT Outpost cro-moly frame that is definitely 1".
Basically just a parts bike, but it sure did ride great.