Been a long time- as I recall the mountain bike cups had the bearings set deeper to centerline as there was a “rubber” seal - is that the cup type you have?
campagnolo did some odd bearing dimensioning to the bottom brackets in the mid later 80’s...
keep in mind, mtb bottom brackets were wider too 73mm
i think you need a matched set of bottom bracket parts- what is the crank date code on the drive side?