Doug's D308's fit perfectly in my 69 SS 350. No dimpling and had clearance around the PS box. They are 1 5/8" tubes.

 

For a car that is 42 years old and has probably been messed with many times over the years, I have a hunch that the wrong engine mounts might have been installed somewhere in the past?

I've never really seen this problem with Hookers and small blocks.

I know with big blocks, lots of problems with Hooker headers are solved by installing the correct engine mounts. It's a very common and overlooked solution. Not saying that it definitely is in your case, but I'm just putting it out there so if people do a search on the same problem in the future, this info will be here for them