Another option (and old hot rodder's trick) is the late 33-4 box; 15:1 ratio and is easily adapted to the A chassis by using the A sector housing. Length is 42", (about 1-2" shorter than the A shaft) so it'll buy you some room when/if the "middle age" spread kicks in
The A steering mast could also be adapted pretty easily (you'd just need to bush the A mast to fit the smaller 33-34 upper race cover).