Rear wheel and tire combo ???
I'm not sure of the wheel well differences between '69 and '70 so take your chances.
69_340_GTS- Not sure if you have a typo. Mine were
255/60-15.
ChichliDart-I posted a link to my original setup. My fronts were 14".
Rocky-The 255s had about 1/2-3/4" clearance with everything stock. I have clearance pics if needed.
http://www.forabodiesonly.com/mopar/showpost.php?p=1970477246&postcount=496