In reply to Rick Wicklin.

layout overlay3d/
zaxisopts=(griddisplay=on labelattrs=(size=12) TICKVALUEATTRS=(size=12)
LINEAROPTS=(TICKVALUELIST=(0 20 40 60 80 100) TICKVALUEPRIORITY=TRUE))
xaxisopts=(griddisplay=on labelattrs=(size=12) TICKVALUEATTRS=(size=12))
yaxisopts=(griddisplay=on labelattrs=(size=12) TICKVALUEATTRS=(size=12));

Done! A lot of thanks...