Is This Stamp Possibly A 279Be?

It looks like it's from a booklet pane and from the looks of the right side roughness that it could be a 279Be. I am probably totally wrong, but I am very confused with the variations on this issue and any help would be appreciated. For reference this is on a cover dated June 8, 1903 Pueblo Colorado.

Short answer: Booklet, yes. 279Be, no.

Longer answer: The plate layouts for booklets are shown in the intro pages of the booklet section of the Scott Specialized catalog. The 180-subject plate includes a perforated guide line across the center of the plate which falls within the central row of finished panes. The guide lines on the plates for sheet stamps were not perforated, only cut. Thus your stamp showing the perforated guide line can ONLY be from a booklet. Note the line on the lower left perf extends leftward beyond the left edge of the stamp, so the red on the perf tips cannot be from the stamp below, but only from a guide line.

All that said, 279Be is only a sheet format stamp, so yours must be another sub-number. Your choices would be 279Bj (a 360-subject plate, which does not have the guide line fall within the panes) or 279Bk (a-180 subject plate, discussed before). The perforated line proves your single is from a booklet of 279Bk, if I read my catalog correctly.

Add: here are two used pairs straddling the guideline reconstructed into a block, 2/3 of a pane. Yours would obviously correspond to the upper right stamp.

John, thank you. Greatly appreciated.