From what I have measured for mine, I came up with a wheel well width of 11" to 11 1/2" . A 10" centered in the well will give you approximately a 1/2" clearance on each side. You will still have to take in the offset of the wheel to determine if you can get a full 10" and how deep you can go up in the well with out having rubbing issues. Tremec has a good gear ratio calculator that also does tire sizes at the bottom. which will help you dial in a tire size. I looked at an 18' for me and came up with 245/65R18, which gives me a 30.5" tall and 9.6" wide tire wheel combo. I am keeping it at stock height.

1950 3100 with a 1962 235 and a SM420 4sp trans