Check with Mike on the diff cases but I believe yes.
Go with the:
- traxxas extended rear revo arms
http://www.rc-monster.com/proddetail.php?prod=TRX5333R
- RP front arms (only if using stock plastic drive shafts)
Best confirm about the BK and Medusa compatability in brushless section I'm not sure
610i It has a lower power rating 250w but at 25V this is still 10a which is enough for a 2p pack - It has a built in balancer for when you do an occasional balance charge
http://b-p-p.com/proddetail.php?prod=fb_0610i
The 1210 requires an LBA10 external balancer.