Magnum 5.2 & Doug's D453 Header Fitment Issues

One FIRST thing I'd do is obtain, from a member, a "stock" V8 install dimension from say, the front wall of the crossmember to a known point, such as the rear of the engine bell face, or such that you can access, to establish the stock front/ rear dimension of the engine as in place. This should not change. If, example, you had a stock trans, such as a 904, etc, you could locate the rear mount "as original" and that would be that. I don't know if the 42XX are the same dimension, etc.

(I cannot tell you that because mine is apart)

I assume the Shoe mounts came with destructions as to how they are oriented etc? I don't remember the years, there are truck pillow mounts that are thicker than 67. I tried to use them on my 67 with stock mounts but they were too tall. In your case they may be what you eed