ive actually done it a few times in a swingarm 150. the 1st time in a yerf, the second in a crossfire and the last one, recently in a yerf which is in a thread here. the 1st two are on the other forum site and if you do a search on "baby huey" should come up for the 1st yerf build. i only bring that up because the swingarm was used from that build on this most recent one on the thread here, so any details on the swingarm fab arent in there. search "crossfire 250r" on the other site for the crossfire.
basically the 2 250 versions that we see in our buggies are usually both made (the chinese versions) by the company CF MOTO, so either or might be considered CF250s. commonly what i have found is that on the buggy forums the one that requires an external gear box of some sort is referred to as a CN250 and the one w/ built in reverse and the hi/lo is referred to as a CF250. but like i said they are both built by CF MOTO. i think the hi/lo motor is referred to as the CF is because it usually has the name of the company somewhere on the motor where the other version usually doesnt. where the "CN" comes from is on the motor w/out the internal rev/hi/lo is a carbon copy of the Honda CN250 Helix scooter motor. so basically these have been the adopted names to differentiate the 2 250s.
as far as mods to the buggy the biggest thing will be the swingarm. obviously, you'll have to fab a new mount for the front of the motor and rear of the motor . the rear mount will be to have a chain adjustment which can be similar to a 150. mounting the back of the 250 is critical. i have broken the case of the motor having the rear mount to far back behind the motor which wasnt really a whole lot. you also have to take into consideration that the carb is front mounted so when redesigning the swingarm leave some space for the protruding air filter.
mounting a radiator will also come into play.
then last is wiring. if you are experienced and have done a 150 befroe there are some differences. you will need the proper rectifier and cdi which are specific, where as the solenoid and coil can be pretty much universal so the existing 150 stuff would work.
that will get you swapped. then you will probably want to do some suspension work to compensate for the added speed.
o also have facebook photo albums which catalog every build i have done so if that helps feel free to look or send a friend request.
good luck, hope that sums it up.
https://www.facebook.com/jerseydevil.minibuggypage