[1795]

Taking a look at CompClassics advice and the pictures of your floor pan and mine, I have a lot more room between the sides of the floor pan and the transmission tail housing than you do. My opening looks to be a couple of inches wider. That may be the problem. If your engine is centered and as far forward as it can go to allow for clearance with the radiator and to change belts, etc., then it may be that the tunnel opening is too narrow/floor pans too wide.