If it were me, I'd get radial tires. Do the math, load C may be sufficient.
Do NOT mix radial and bias ply tires. By design, radials grip better than bias ply. So what happens is, on a curve for example the bias want to slip or give and the radials don't and it can cause a skid type situation easier than if they are all radials or all bias ply. In essence, the radials act like a pivot point and the bias want to slip around the pivot point.
This issue is not as severs as compared to a vehicle as it is being pulled and things want to stay in line. On a car, it causes spin outs.