Searched around a little but couldn't find what I was looking for.  I have a flat-top M4 build that needs a new upper receiver.  I was thinking about replacing the flat-top with an A1 upper.   The gun already has an old school Colt Type 1 stock on it, so I think it will make for a nice KISS rifle.  Just looking for some pics if anyone has one set up like this.  Also, would this be pretty similar to what the IDF uses / used?  I don't know much about them.  Did our military ever use M4 barrels on A1 receivers?  TIA

Not an A1 upper, but a 604 upper (lacks forward assist). I believe I have seen A1 uppers (forward assist) with M4 profile barrels before, though.

Model 723 from the Retro forum

It has a standard front sight base, not F marked.  It's a RRA barrel.  

Thanks, I was wondering if it had a specific model number, so that answers that question.  I see that one has the smaller handguards, I have a spare set I could put on to make it more "correct"