Another rear tire size question and advice needed.

Need some advice on rear tires for my 73 Plymouth.Duster I currently have l60 15 On the rear now , with 15x8 4.5 rally wheels with a one inch spacer. I want to remove the spacer and put The widest tire I can Without it hitting the inner lip on the rear quarter. New rear springs and shocks...no air shocks...using longer shackles..at the moment.. i want to use stock shackles...ive done several searches for tires sizes and they are all over the place. I read a 255 60 15 or 235 60 15 .275 60 15...would work.. Advice would be appreciated
1972 Duster. 275-60-15 on 15x8 w/4.5 works perfect. I'm all stock, no cutting, no spring relocation or SS springs and no air shocks. Fit perfectly and don't rub, even hitting train tracks at the 30mph.

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