Don't discount those 421's, especially in a plain old reflex box. In the 828's, for hifi, the 421's aluminum domes would need to be damped, or replaced with a paper version. If you seal off the 421's rear vent, and install vented Altec dustcaps, they will look "right".
GPA diaphragms have taken a good hike in price, Radian 1228's are a bit less costly, more robust than the all aluminum 802 diaphragm, built similarly to the Altec Symbiotik, and sound very good.