bullit, is the C-4 also an 1985 unit? if oyu can get your hands on a B&M catalog or check on line. look at the holeshot torque converter section, they have a good listing of the C-4 converter size differences and then you will know which flex you need. a 10.5 bolt cicle converter uses a 157 tooth, the 11.75 bolt cicle convertr = 164. also you can tell by the bellhousing. if there is a gap between the bell housing and the trans that is the stepped C-4 =157. that is usually early c-4.
i kow it is a hassle when you dont know but you need to find out.