Not sure what they are referring to, but the F100/F150 rims will obviously fit the F100 hubs! I have never had any problem with any rim fitting. Maybe they are saying 30s factory wire wheels and 5-wide, etc. No idea what disc brake rims would have to do with it. This conversion uses all original Ford parts, the only modification is to the inter bearing on the hub. It has been done thousands of times starting in the 50s.
OK, the Speedway kit in question is a disc brake kit, not the F100 conversion kit! Here is the link: http://static.speedwaymotors.com/pdf/91031909pdf.pdf
barnfind was 100% connect (no surprise there!) and was directing his response to 39 Portlander (as he clearly posted), my error.