Just out of curiosity... why 'not' heat treat?
I'm actually kind of surprised your rifle is holding head space with no heat treat on it. (..is it maintaining head space? are you checking to see if it's growing with a complete set of gauges?) I've fired less than a mag on a raw receiver and had the head space grow considerably (not something I would recommend) You don't have to heat treat the entire receiver like DSA... I think the Austrians just spot treated their receivers. The area that takes the beating is around the locking shoulder. The shoulder itself won't deform (because it's heat treated) but the receiver in that area won't hold up.
I'm not here to preach or anything, either way it's nothing to me personally... just throwing out some info I've gained. Also, I've had an FAL fly apart on me due to bad ammo... and I can say definitively that it's not a recommended experience.
Someone said something about a receiver stub... I have some pics if that helps.