Been there, done that. There are two paths to take - one is to simply replace everything with an equivalent item with the larger fixing. And if you are selling your older (smaller) lathe, the purchaser might appreciate getting those fixings with it.
The other is to look for adapters like the one Elwin suggested. My scroll chuck was designed with a native 1"x8tpi threading and required a 3/4"c16tpi adapter for the old lathe - so I just removed the adapter. I bought an MT1 to MT2 adapter sleeve so that I could continue to use my pen mandrel (which I don't use very often), and a spindle adaptor that allows me to continue to use stuff designed for a 3/4"x18tpi thread on the 1"x8tpi spindle of my new lathe. I also found that rather than buying a new MT2 jacobs chuck, I could buy a replacement arbor with an MT2 taper at one end and at JT33 taper at the end that fits into the old chuck body.
The only downside of using adapters is that adding an additional gadget could potentially increase runout, but my experience was that this was not a significant problem.
