340 in early abody

An early A kickdown linkage works fine on your 904- others can be made to work. Otherwise use a cable linkage, Bouchillon makes a good kit using the Magnum cable. No need to go full manual if you don't want to.
Most passcar pans for 273/318/340 (NOT 360) will work, but may require a dimple in the pan to clear the steering at full lock. Some pans already have this, not sure of the number. I'm sure somebody will chime in with that.
Hood clearance will be tight, especially if you have to start shimming your motor mounts for header clearance/fitment.