This was years ago, but I learned back then to never mix bias ply and radials on a smaller truck (Pick-ups and 1-Tons), but it is OK on a larger truck (2-Ton or larger). I had a '67 GMC 7500 (Class 7 Truck) and got the OK when I asked about running bias ply on the front and radials on the back. Altho I personally prefer one or the other on both axels.
Bill