I know Raptor, I was thinking of PM'ing you for details of your setup that you have posted before.
As for the handguard solution, far cheaper then a new barrel assembly, but the factory handguards are so awesome and I grip them rather forward.
I was thinking of machining the mesa clamp down so that it basically exclusively clamps on the barrel and barely touches the tube just for indexing purposes.
The clamp just puts the light in the perfect position (for me at least.)
The biggest problem with that, is since the barrel has a heavy taper, unless you put the light mount right in the middle section of the barrel where the taper stops (and it starts to get bigger for the choke) it will slip around under recoil. A few shots and it may loosen up enough to freely move back and forth. I tried cutting the bottom clamp section off the one I had but it didn't want to hold in place properly
I tried to design a picatinny rail section to replace the front sling plate, and would be usable in 3 different positions (a 6-oclock, a 10 o clock and a 2 o clock), but when I bend the sheet metal portion over, it was too flimsy and would bend under impact.
Granted, the sheet metal I used was from a cheap-o gate hinge from Canadian tire, so maybe using a higher grade of spring steel would be better....
This was as far as I got before testing it proved to be not strong enough, although it did fit fine.
ETA
This ended up being my final solution though: (took a lot of work to get the steel insert on the inside to get thin enough to actually fit the mag tube. Had to be less than 1mm thick)
Brownells sells a cheap, 3 rail aluminum picatinny mount which clamps around the mag tube just ahead of the sling attachment.
I had this on my M4 and had an M3X light attached, worked great. The upside is that there's no need to drill holes. The only downside is that it has to be removed/loosened to disassemble the gun.
I had the Insight Technologies mag tube mount, and it actually worked really good, EXCEPT that it had to be removed to field strip the gun. That was the only downside, I did try and put it on the faux extension so I could unscrew it, but I hate tape switches and couldn't get used to using it like that.