See, the cap at the front of the triangle handgaurds is triangular, and I just assume that the cap at the front end of current-production guards would be circular.  Am I correct?

So, would current production (A2) handguards be compatible with the hardware on my A1 upper if I chose to change from the triangular handguards currently on it?  In other words - could I just swap the two plastic pieces out and everything else be fine?  

The A2 uses the triangular handguard cap just like your A1 does, so yes, you can interchange handguards with no problem. BTW, the A2 handguards will also work with the round end cap.

A2 circular handguards will fit on triangular handguard caps but triangular handguards will not fit on A2 circular handguard caps.