The dash has no positive location marking on the interior tub, and where one thinks it's the right spot, usually is too high. That causes all the problems. What I do is first install the glass to the body, then glue the dash to the body, making sure the doors can open and close, and just then I place the interior tube on the body. The only hard part is having the steering column in a good position before installing the interior or it will interfere with the fit.
Learned this trick with the AMT '57 Ford kit.