4age would be the easiest cost effective to end power result. I wouldn't waste my time with a 3t efi, its 30 year old technology, sohc and pushrods. Anything thats a straight 6 cyl would also be a waste of time if your not going turbo, all that weight over the front wheel's will destroy the handling characteristics when you could achieve the same power to weight ratio with a 4cyl.
My advice for a decent n/a cost effective swap, ca18de?