Need advice on tire/rim size for my 69 cuda

Absolutely no way in hell will a 235-70-15 (28") fit on the front so we can scratch that tire off the list right away.

Your safest bet for the front will be a 215-60-15 (25.2"), maybe a 225-60-15 (25.6") if you are willing to trim the fender.

Another front option may be a 215-65-15 (25.9"). On paper it should work but in practice it may not.

For the rear, the 255-70-15 you selected is very tall (almost 30"). A 255-60-15 would be a better choice at 27" tall.

The factory tire was just under 26".