That's a bad leak! Like you did not know LOL. I am suspecting something other than just gaskets.
Question #1: Were there alignment pins in the front and back end rails? If so, and you did not pull them out, or drill matching recesses in the new intake, then the rear of the manifold may simply be jacked up and not sealing at all.
I broke a cast iron 273/4 intake because I didnt notice the dowels in the 318 block I was bolting it down onto. I think it would crack under 35 ft/lbs torque on the bolts?>
