FWIW, If you're going from the top with an assembly, pull the distributor.
Another option is to raise the rear of the car to cut some of the assembled angle.
On a big block, a deep oil pan may cause an assembly to be tight between the firewall and K-member.
I'm no body guy but I'll cite an observation from your OP picture.
Maybe it's a clue or no help at all but it appears your passenger side fender may be further forward than the driver side............
Same on '71 but omits "-3-2 bbl." wording.
If it helps, this is the 6 quart pan dimensions. Is this what you have?
If yes, IMO, just run 6-1/2 quarts, remark the stick and drive the wheels off it!:steering:
Some good reference in these for beginners....
https://www.forbbodiesonly.com/moparforum/threads/8th-edition-mopar-engines-book.309730/
Manual downloads here.......
https://mymopar.com/chrysler-master-tech-service-library-browse-model-year/
I wouldn't use that pickup as is. Bending the bottom to conform might breach the screen and allow too large of particle into the pump and lock it up.
I might try bending the tube a bit out of the engine. I'm not suggesting you try that though.
Maybe someone else has dealt with this and will...
Yikes, that's a bunch off level. Is that a straight tube pickup?
You might consider a different pickup......
https://www.manciniracing.com/mara402oilpa.html