Can you install a Brownells A1 barrel assembly into a A2 upper receiver? Would it work together?
Thanks

yes it will work.  only thing to check is the barrel extension, if it has rifle feedramps and the a2 upper has m4 feedramps, you *may* run into feeding issues.  any other combination of feedramps/uppers should be ok.

Brownells barrels have the rifle feedramps, not the m4 style. So I guess it wouldn't work.

A standard M16A2 also has rifle feed ramps, so they should work fine with a standard A2 type upper.  If you have M4 style feed ramps in your upper, then look for a barrel with M4 feed ramps.

This.

The only problem i would see with a A2 receiver that has normal rifle feed in a A1 barrel assembly with standard rifle feed ramps is the iron sights may be difficult to zero and use correctly?

The A1 and A2 use the same height sights and it wouldn't make a difference in which one you use.  As far as left and right, all barrels index off the receiver in the same location so theoretically should be the same from an A1-A2-M4 etc.  But shorter barrels like the M4's tend to come with an F marked FSB which just sits the front sight post a few mm taller then the others.  This isn't even really needed on the majority of rifles, but sometimes a front sight would have to be maxed out to zero so they ended up just making the base a tad taller and that is where the F marked FSB came from.  But the A1 and A2 both have the same height sights.  And the majority of the time you should have no issues using a non F marked FSB on a newer M4 type rifle or vice versa.