Playing piano ON a piano is not a necessity, Don. In fact, the vast majority of piano parts can be played on a 76 without very little adjustment (it's amazing how in most pop, you rarely stray outside the 76 range - in fact, back in Mozart's day, he played on a MUCH smaller piano, so a lot of early classical doesn't need 76 either!).

But working on the LH is the main thing. No longer do block chords suffice. Lines, arpeggios, all that stuff you've spent a lifetime on in the RH now matters. Thing is, leaving it until so late in your career is pretty tough. A lot of hand strength and especially stamina takes time to develop. As adults, we always expect to get somewhere significant very fast, and trouble is, this takes years of patience. As kids, at our fastest learning rate in our lives, it still takes patience and years... Why we expect, as adults, to do this in a month beats me!

Baby steps, over years... that's how you do it!

Mind you, on the other end of the scale, I also recommend any piano player that HASN'T played an accordion, or a full organ, etc., to also try to play these too. Every single thing we do opens up new possibilities, new techniques, and those enrich our playing and our lives in ways we can never tell in advance.

Don't close yourself off to anything.