The difference between a 230 and a 250 is the stroke. A 230 has a 3.25" stroke while a 250 has a 3.53" stroke. Both have a 3.875" bore.
I've never done it, but I'd figger that you'd need to use the 250's crank, pistons and rods to make the conversion. The head should bolt on just fine.
They question is "why?" The advertised HP difference is only 15, same for torque. If you want to step up in power, a 292 would be a better choice, imo. Yeah, there would be a little more work with the motor mounts, but you'd sure get a whole lot more torque outta the deal. I love my 292, btw.