yeh, get them tuned. Also, try changing the exhaust though that might not be that big a difference.
dunno what k motor nuts told you 40s are too big, there's plenty of people around the place running them with great success.
Also, I wouldnt bother putting a good set of twins on a blower setup for drawthrough. The money you could sell the twins for would fund a weber downdraft blowthrough turbo setup!