Using the X & Y feeds automatically gives you rivet lines at 90 deg or you can add further rows exactly parallel to each other. Using the top slide swivel gives you lines at almost any angle to each other, such as diagonal rivet lines on tender tank sides.
I have a special sheet metal clamp that fits directly onto the tool post stud.
I face trued a 4" diam disc permanently fixed to a mandrel; this is then mounted in the 3 jaw. With the tool post stud slack, wind the saddle up to the chuck, align the edge of the sheet metal against the disc then tighten the tool post stud = automatic setting at 90 deg to the lathe bed & lead screw.
(I used to be lead machinist in heritage railway machine shop so I dream up these things in my sleep !).
Once set up, which is a bit time consuming, then riveting speed is only limited by how fast you can swing the riveter handle & count the fractional fine feed turns on the X, Y handles.
-ex Rivet Counter (that's why I've turned to US On30 - to ENJOY railway modelling)
-- let Bachmann & MMI/PSC etc take the strain before I reach my ga-ga years.