Thank you, thank you !
The grip is now on... and fits great.
Having installed this beast , I can say that the correct method is 'E' all of the above.
I took a file and cut down the inside top edges until the grip would slide over the back end of the rail and tapped it forward using a rubber mallet. But when I installed the rail strip to the bottom of the SIR handguard , the grip's inside wedged against the lower handguard, not allowing the SIR strip to sit flush on the bottom of the SIR lower guard. So, out comes the dremel with an old worn-out cutting disc. I cutoff about 1/16" on the inside of the top of the grip where it touched the handguard.
Screwed the rail strip down, tapped the grip forward, covering the rear screw and it clicked into place. Perfect fit now.
Thank you gentlemen for all the good suggestions! I needed them all.
I'm relatively new to posting here, but have been shooting, banging, grinding and tapping on AR's and M-16's for 27 years now. The more I learn , the more I realize how little I know about some of the newer accoutrements!
Thanks, Jay