if you can take your gas block & tube off, you can rotate the URX off like a URX 4 -- you can even use the URX 4 tool without the plastic insert (with maybe a little masking tape on the handguard). hold the upper horizontally in the vice using something like the following:
once the handguard is off, it is usually easy to rotate the steel nut off with a long punch. once the nut is off, overhand throw it into a lake and get an aluminum nut.
(last post ever -- i swear. i couldn't resist. i have my 14.5" SR-25 and my life is complete.)