>Scrollbar width and height I can get through SYSMETRIC()
>the width of grid lines can be retrieved from GridLineWidth property of the grid.
>Anybody know off the top of their head if there's a constant or function that I can use that gives me the widths of the RecordMark and DeleteMark (if enabled) in a grid?

It is fixed.
RecordMark = 10 pixels
DeleteMark = 8 pixels

you can measure it with delta position of left visible column

OBJTOCLIENT(thisform.grid1.column1,2)