Could you (and this might sound dumb, I don't have a v6) run it for a few minutes with the valve covers off?
Or cut the tops out of a set of sacrificial covers?

Or, can you (again, I dunno anything about v6) run the oil pump by its self, like on the 216-235 (pull out dizzy)

Then you could see the oil dripping out.

Christopher
1950 1-Ton
"Rochester"
In the Gallery
In the DITY Gallery

1949 GMC Panel Truck
1926 Model TT Truck