I have a set of voodoo2's but three not the same card
one is a 8mb CT6670 and the other is a v2 1000 12mb with memory chips on the front side only

can I sli these?
I know that 8mb and 12mb have been sil'd before but the second card on'y uses 8mb of its ram

it's not recommended-you will need a lot of luck and drivers with mismatched support.