B2B
I fitted an O-320 B2B conical mount to my 9A. You are right about the carb being too far back. This would work on a taildragger but not on an A model.
Since I got such a good deal on the engine, I decided to swap out the sump. It was a really easy thing to do and it cost me about $400.
You get a sump that moves the carb forward. Then, you have to change the way the oil is picked up from that sump. The stock set up has a pick up tube extend down into the sump. The mod removes that tube. The new oil pick up point is from the bottom of the sump and then up through the walls of the new sump. You also have to change the intake tubes.
Believe me, it is VERY easy. I stressed about this for a year before I actually got around to it and it was cake.
I got all my parts, except for the sump, from Mattituck. They were very helpful.
Find yourself a parts manual and check out the two different kinds of sumps and oil pick ups. Also, check on VAF for my posts on this. I think I included pictures.
As far as the mags, I have the mondo sized Bendix mags and they clear the conical mount just fine. You do have to remove them to remove or install the engine though but no big deal.
I'd think that your B2C takes conical mounts as well.
If you want some pix PM me.
Oh, and to figure out just what models fit without modification, refer to the parts manual. You'll see a table there with engine model numbers. The models that use the forward carb sump are the ones that work.