If you don't mind going the pusher route on the electrics, I have found that twin electrics fit perfectly into the core support on a '68 from the front side of the radiator. It also gives you plenty of room betwwen the radiator and your motor. You can also mount them as pullers and they work great too, but I like the fact that they fit into the support so perfectly on the other side.
http://i226.photobucket.com/albums/d...own68/fans.jpg
Flex-a-lite twin electric
Flex-a-lite Low Profile Electric Fans: FLX-210 - summitracing.com