What mastercam version ?
What modified post ?
"arcoutput" should be found in the general output settings near the top of the PST file
looks something like this
If version X or later
breakarcs : 0 #Break arcs, 0 = no, 1 = quadrants, 2 = 180deg. max arcs
arcoutput : 2 #0 = IJK, 1 = R no sign, 2 = R signed neg. over 180
There is also an area in the MD ( Machine Definition ) file that requires setting, under "arcs"
PS: a mastercam forum exists, overseen by those working Mcam
you would get better / more responses asking the question there.