Mike P - changing the gap on your points is how you adjust the timing. Mike G pointed out previously that setting the points at the Kohler spec of .020 hardly ever gets the timing correct. .020 is usually a good starting point to get a unit running so you can set the timing with the active timing method (timing light) which I prefer. In your case with backfiring you need to use the static method (which many believe is extremely accurate). You really need to make sure the timing is correct which ever method you use.
(under edit - I see Ron S beat me to the post)
Amy, Amy, Amy - your blondeness is coming out. I do think you learned something but maybe my info didn't provide enough details. Narrow frames refer to the early IHCC units that are approx 11" wide across the front of the frame. For instance, the 71, 102, 122 and 123 are early narrow frame units. It's easy to decifer exactly what the model is by looking at the model number, i.e. - if the last digit is an even number (in your case a 2) then it's a gear drive unit, and the 2 digits before that identify the engine hp (in your case 10hp). This works for all the units except the 2 digit 7hp units which are all gear drive and just numbered consecutively. The 1x8/1x9 series introduced the wide frame or WF where the frame is spread to approx 13" at the front of the tractor. IH did this to accomodate the bigger hp engines like 14hp and 16hp. The WF designations still identify the type of tractor and hp, i.e. - a 149 is a hydro unit since the last digit is an odd number, and the 14 identifies the hp of the engine. Nothing in any of the designations identifies it as a NF or WF. You just have to know which series is which.
Hope this helps.