From what I've seen/read up on a standard roundie front isnt big enough for a b series and thats why most people use clubbies.
Have you seen the project binki build on youtube?
Those guys are using a complete celica gt4 engine and full running gear into a mini so anything can be done depending on how you want to go about it.
The other guy in Victoria with a b16a clubman, I'll try find his contact details for you
Check project binki on youtube I, recommend it to everyone