I got the UFO megaphone w/both size endcaps for my UFO 4/1 Dragstar. Yes, the megaphone is less dB than the bologna-cut end piece which the Dragstar comes with, but it's still loud, whatever size the end cap diameter opening.
Trying to change-out an endcap to satisfy a LEO on the side of the road is probably going to be very amusing for the LEO and painful due to hand trauma from burns for you! A larger-volume canister than either the UFO bologna-tip or the UFO megaphone replacement is what I would recommend. Make your own like I did, or get one from Sean, Mark's Exhausts, Kyle, or whoever.
Right-now I am selling a Kerker header and mid-pipe to another member, just waiting on final payment, it was in the
parts for sale section. Grab a used can from somewhere, and you would have plenty of dosh in the ol' bank account for airbox and carb mods.
Kyle and I both run Stage 7 and VBoost w/aftermarket full exhausts. It's much-easier to synch carbs w/VBoost intact, instead of removing it like the Dynojet Stage 7 directions have you do, something to consider.
I think Supertrapp (which now owns Kerker, I think) sells some-sort of variable-opening end cap, which might be what you're looking for, kinda like an old-time Snuff-R-Not that I ran on my Honda 305 Scrambler, my first bike I bought 43 years-ago. Try this site:
http://www.supertrapp.com/product_sections/acc/access.asp
I was a little concerned with the noise factor, there pretty strict over here ticketing harleys all the time. I thought the ufo`s have end caps that can be fitted to reduce this down? if I kept em in my bag and got pulled over I could just screw em on??
I plan on getting the stage 7 kit plus Morelys airbox kit along with the exhaust/headers, tryin to get all that under $1200.
Does a 4-1 make a little more power over a 4-2? I did not know that