8 3/4 bbp on my 67 dart

my 68 dart is the same way-- a little tighter on the one side than the other. it's just production tolerances from when they're built.

1- 245's is about as big as you can go with "production/factory" parts-- ie stock a-body 8.75, big bolt brakes, 7" rim with 4.25 BS
2- the offset of BBP axles and discs add to the width. if you didn't account for this then that would likely be the difference and why you're having fitment issues.

possible remedies:
>roll the wheel lips, maybe push the sheet metal out a hair
>smaller tires
>rims with more offset
>reset/reposition the axle