I just installed a 261 engine in my 1959 3100. The problem that I'm having is that I cannot get the clutch adjusted to let me go from neutral to first or reverse without excessive gear grinding. The 261 was removed from a 1959 C60 with no change to the clutch, pressure plate or throw out bearing. The clutch and pressure plate is the three finger coil spring type for the 2 and 2 1/2 ton trucks. I had no shifting or grinding problem when it was in the C60. I now have the original 3 speed transmission behind the 261. Do you think the 3 speed input shaft doesn't have enough resistence as compared to the SM 420 to stop the clutch plate from turning in neutral or should I replace the coil spring clutch and pressure plate with the diaphram type?