Altec Model 19 - which caps for crossovers

not sure what you mean by altering....if the old capacitors are aged and not holding the values changing them "sensible" alternative is the only way to re-surrect the speakers to its "original" sound....

if you are over it with the "authenticity" issue....you may also try old Vishay MKP series.........we will never know, how the old original sounded anyway, nobody has such a memory and these older caps are long gone, nobody makes them anymore, so what other choice you have?

I did upgrade them with Jantzen Cross Caps.....easy to do and excellent results!