1963 Step side tires sizing.

[transoceanic]

Looking at getting larger wheels to change the stance and fill the wheel wells. I'm looking at 18" as I still want some sidewall on the tires. I know the rear size is the important one due to limited space. I am also wanting to gain some height in the front as my lower control arms are too low. The truck currently has 245/60r15 in the rear and 215/60r15 n the front. the front tires are are currently 25.52" tall. If I go with 245/60r18 front and rear that gives me a 29.6" tall tire. Around a 2" height gain for the front and 1.5" for the rear. I have been looking at a lot of trucks and I like the look with the tires the same front and rear? For the rear I am assuming, if a 245/60/15 tire currently fits a 245/60/18 should work as well???? Added a picture of the look I am trying to get? I know they are 20"s I would just have a larger side wall.
Any thoughts and recommendations welcome.Thanks

[transoceanic]

After reading my post , it looks like I did not make my question clear.
Asking for help from stepside owners who have 18" wheels on :
back spacing and tire size.
Thanks
Ted