In addition to being strong enough to hold the boat, the other key consideration would be that the cradle pads contact the hull in the right places. Typically, where there a bulkheads.
So, Catalina would be the place where I'd start for a set of measured drawings to turn over to a welder.
If Catalina doesn't help, it wouldn't be all that difficult to create a measured drawing if there is a 320 cradle somewhere in your area. Measurements and photos should be enough for a welder to make one for you.