The prop had seven "grips", approx 96 mm long. The 7x3.625 grips are closest.
You could also get some longer grips and cut them. I find it easiest to cut the notch straight across with the grip laying down with a thin piece of wood as support.
To avoid flare over the pommel:
Get 1/2" double sided tape that has some thickness to it.
For each grip cut a piece of the double-sided tape that is 3/4" shorter than the grip. Remove the paper from the grip and attach the strip of tape, with its paper still attached. Then rub off the glue on the back of the grip with your fingers.
Next, if your tape is not black, take a permanent marker pen and blacken the sides of the tape.
Now, the grip would attach only to the flash tube and is lifted over the pommel. I think it looks best if it does not attach to the pommel.
To line them up:
Looking from the bottom, one grip should almost line up with the bulb release but be slightly to the right. The clamp should line up with the grip closest to the 7 o'clock position.
You can download a grip spacing template from www.partsofsw.com (click on Item->Darth Vader's lightsaber->ANH->Grip spacing template at the bottom).
btw. There is a tutorial thread on Rebelscum's msgboard right now that tells how to get correct spacing between grips.
Actually, I prefer the "grips" that came with my Parks MPP over the grips I got from Blast-Tech, because my Blast-Tech grips have some shrinkage in the middle of the fin.
The real "grips" had slightly angled fins with rounded fillet at the bottom, quite the opposite to Blast-Tech's. Nobody has made perfectly accurate grips yet, but I will replace mine when that time comes.