273 to 383 swap
Nope, the mounts did nothing to change the location of the transmission
(a-bodies use the same trans mount no matter which engine or transmission). The trans tunnel was enlarged at the beginning of the 1967 model year to make room for the big block and 727 (and likely they already knew the 340 was coming in 1968 ). The reason for the huge change to the location of the driver side mount was to use the 1965 C-body mount which mounts to the front of the block and the forward boss on the side of the motor.