Assuming you've already got the dropped V8 centerlink.
The 340 can use an original A body 273 pan which has indentations on the bottom edges to clear the pitman and tie rod ends at full lock- sorry I don't have the pan number offhand, and there may be others that work.
LA 360s and Magnums can't use those pans because of the end seal diameter being different. They require use of a 360 pass. car pan- most use a "392" pan, although it MAY need to be clearanced with a BFH to resemble the 273 pan. Or shim the motor mounts a bit, or combination of the above...