from what i've been reading around here is that springer forks ain't all they're cracked up to be for motorizing.
those cool looking monark repro's up there that barelyawake posted? well, everyone i've asked that uses them has said they tighten them down so much that the spring is about useless.
the "lowrider style" schwinn repro forks look like they were built out of a screen door, using a vice and a hammer as the tooling mechanism. i wouldn't even trust those on a bike without the motor. in fact, if they were still a screen door, i'd be afraid it'd slam in my face.
mountain bike suspension forks may be the way to go, but i wouldn't know, they'd look goofy on my bike.
it's kinda cool how much regular forks flex when you're hammering down the street. they'll move 4 to 6 inches forward and back. and from some research i've been doing, they're supposed to.
so, uh, i dunno. i don't think i answered your question...