I would also comment that years ago we 9 being a grup of50 or so) experienced 2 issues with the 273 rockers on a 340/360.
1. The 340's had a larger valve spring/ retainer. This would interfere with the rocker in the area circled. a couple of passes on the grinding wheel would usually fix the issue
2. They were prone to bending at anything above a stock 340 valve spring pressure.

Another tidbit on rocker arms. The early 68 340's used stamped 318 rocker arms. It was soon discovered that they had the same clearance retainer issue. The motors ran fine but would lay down a bit at upper RPMS. When this was discovered the rockers were revised and actually had a grinding mark visible on the later 68 motors. I might have a couple of each laying around but would have to dig for them.
So if any have an early 68 motor untouched you might want to check the clearance. Somewhere in the 69 to early 70's the stamping die was apparently changed to allow the needed clearance. See pic's