I have V1.5, so similar but different than yours. The A55 is a problem with the k53 being bolt on, I haven’t found an adapter yet. I bought ALK universal x-over, very nice sound. Swapped out K22k woofer (not sure what you have for woofers) for B&C 12CL76, also nice. Seal the interior seams, neoprene all interior including motor board and rear door, new 5 way binding posts and 12awg interior cables. That’s a good start! Rejuvenate the veneer (good to begin, better now) e.g. with Howard or Watco. I need to learn more about bracing!
If they sound good now, all i’d really consider is the caps (do you solder?) or full x-over, and take care of the wood.
Re, sub, I have a Velodyne 10DD from great seller on Canada Audio Mart. I am happy with this combo.