Hi there tyrian,
I also have the voodoo 5 gfx card, and have also pondered about replacing the heatsinks, I was tempted to buy two alpha "for general use" heatsinks, but upon further inspection they did not fit. So I abandoned that idea a while ago. You could, however, most probably use a regular northbridge heatsink, and place them on the chips instead of the standard heatsinks, but it's a mild hassle to remove them. If you decide to do this, make sure the new heatsink will fit.
The fans are a bit easier, as they are only screwed against the fins on the heatsinks, so a simple screwdriver should do the trick there (I do it once and a while to clean the fans from dust). You could use a fan bracket of sorts, if you don't like making your own Zalman provides excellent fan brackets that you could use to have a fan blowing downwards on the heatsinks.
For me, I'm patiently awaiting my new components, and after that tuck away my little tbird beast where it won't bother me that much anymore.