Check the middle of this page. Click the trans picture ......
http://www.bigblockdart.com/techpages/4sptech.shtml
I like the MP suggestion of the bell crank being "straight across in any view".
I'd relocate as necessary.
Maybe get a rough measurement of the current seal depth, the axle lip depth after seal removal, and the new seal thickness for reference of install depth.
Don't forget to grease the seal spring so it stays put while installing.
If it helps at all, my old 440 six pack here has a shaker base. I only needed a slight bend to clear the 2 speed.
These other bases would likely need notches for a 440....
The front passenger side should be the tightest for hood to lid clearance due to engine offset.
@ 3:20 in the video you claim the pop was present with the Eddy carb.
That kinda' has me leaning toward an engine issue and not a carb issue.
Maybe disconnect the x pipe and determine whether it pops out one side or both?