How to Fix Passenger Cowl Vent Seal Gap

I currently installing my restored non-AC heater box in my 1970 Duster.The box and blower motor installation went in without any problems. I installed the J bolt on the cowl and through the back of the heater box. After looking closely at the foam cowl seal, I noticed that it is gapping at the front. There isn't any way to clamp the seal and box to the front of the cowl. What's the easiest fix for this? Should I remove the box and add some additional sealing material on top of the cowl seal to help fill the void?