offset shackles (how big a tire)

Thanks for the update.
I’m planning on 245/60x15 on 8” rims with 4 1/2” back space on my ‘66 Dart . I will have to make sure the clearance is there before mounting the tires on the rims . This will be on an 8 1/4” axle .

I currently have 205/65x15 on 7” rims on the rear 7 1/4” axle . Seems like this should work .