Big block bellhousing question

I thought I had this all figured out, but now I'm just more confused. Here's the situation: Putting a 460 and C4 in an 85 mustang. Most people have recommended a pan fill C4. My dad has a 351M bell and transmission that was in a 78 cougar. Now this may sound stupid but I can't tell if it is a pan or case fill? The dipstick goes down the passenger side and seems to go into the case but directly over the pan. I did some research on the web and found the case on the tranny should flare out before it attaches to the bell if it is a pan fill. The one my dad has definately does not flare out. I thought by 78 they were all pan fill, is that wrong? Also if the tranny is case fill will the bell work if I can find another one that is pan fill? And what advantage does the pan fill give me over the case fill? I was told the case fill would give better clearance for headers and such and considering the tight environment its going into, maybe that would be best? Sorry if these seem like simple questions, but I don't know how to find out if I don't ask. Thanks a million.

Jason
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you have a case fill
http://mmerlinn.tripod.com/trans/fdc4f/fd6c4bhm.htm
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Pan fill is stronger and only uses 5 bolts to hold it to the bellhousing. Case fill is for the small blocks and lower HP engines. They use the bolts around the pump area.

Is it possible that this is a FMX as they would have the case fill dipstick and their bellhousings are not the same as C4. Look to see if the case is in fact cast iron and not all aluminum like the C4 is, this will tell you that you have a FMX and not a C4 if it is. Good Luck.

To use a 460 & a C-4 you must use a pan fill trans as the bellhousing bolts to the case, not the pump. Might be a FMX...
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Thanks guys. I think it may indeed be a fmx. I don't guess the bells are interchangable are they?
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Nope.
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anyone use the jw ultrabell? will it fit either trans case?
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