The biggie adapter is used on the 86-87's, because the oil cooler adapter is sandwiched on the oil filter mount. That is why it is shaped like a "sleeve" or spacer. On the 86-87, you'd remove the oil filter adapter, and the oil cooler adapter would come off as well. I think the only way the biggie work on an 85 is if you use the sandwich addapter as well, which means running an oil cooler. Hope that is not confusing...