Snip the cable casing off and get it out of the way. Snap some pics so we can see what's going on. You say the "brass nut part" snapped off, so I'm guessing the threaded part is stuck in the bell housing.
If the threads are stuck in the housing, I'd,,, heat up the remainders of the brass fitting with a torch, soak in PB Blaster, then use left handed drill bits to start drilling the fitting out. Hopefully, it would back itself out with the left handed drill bits. Otherwise, it could get to the point where the fitting is drilled enough to where the threads of the fitting can be picked out of the casting threads.
If you're not comfortable with doing this, but all means, haul it down to the machine shop. Their $50+- charge to remove the fitting is going to be cheaper than if you ruin the housing and need to buy a replacement... Be aware that if the threads need to be cleaned up, this is going to require a special 1/4-18 NPSF tap, don't use a tapered pipe thread tap (something good to know if hauling it down to the machine shop).