Have you pressed the Graflex together completely? When the clamp is loose there should be a little bit of play lengthwise.
I suppose he was thinking of Blast-Tech's rubber T-track which was made to fit against the body of a Graflex flash...
Some people mount T-tracks on their Vader sabers with double-sided foam tape, because it lifts the ends of the tracks over the MPP's endcap . It is not perfectly screen accurate, but it looks neater. The sides of the tape should be blackened with a marker pen first. I don't remember who here that first posted about this trick.
I put some Milliput into the grooves of some T-track I got from Roy, to adapt them to be used with thin double-sided tape on a Graflex, but it was much more difficult to do right than I thought it would be. Some thick glue would be easier.
The original tracks were used for sliding drawers in office furniture. That is why the base is mostly flat. It has been speculated that the groove was intended for a string of glue. Another theory is that it is because if you cut off a section of the fin and drive a screw through the base into the cabinet wall, then the screw might drive up some wood chips that would need some place to go.
Even though the exact type has not been found, at least six other types of plastic furniture tracks have. Some have had an almost-identical groove to the movie-used (and to Roy's) tracks. Others are flat on the bottom or have barbed protrusions to fit into grooves in the cabinet wall.
I think I and he must have referred to the lightsaber that Darth Vader's severed hand is still holding after Luke had cut it off in ROTJ. That lightsaber is definitely a resin-cast, probably of the "Barbican saber" with a couple different greeblies.