67Bob, It'll make a big difference. The chain would have to be made shorter and things will move a bit faster with a smaller sprocket.
I'm lucky in FL that we have Metro Pkwy Industrial complex with several machine shops and that's also where I've had hydraulic cylinders rebuilt. Few people have seen Hi Los, so there is competition on who gets to work with a Hi Lo owner.
Have no idea what it would cost in your neck of the woods, but you may have to have a new one cut at a machine shop. I'd think they'd need the old one as a template of course. I don't think I'd trust a repair on an important item like that.
Tree