I just went through this with my Detroit. There is a bearing that will work to put a v6 differential into a 4cyl housing, however there is no bearing that I could find that will allow the use of a 4cy diff in a v6 housing. I ended up having to order custom bearing spacers from Inchworm. If you have not yet purchased a spool, get the v6 one. That way you can put it in either housing without having to get custom spacers. ARB has the v6 to 4cyl bearings I think they are about $40.
