What u-joint do I have on my 489 case?

I'm in the middle of having my driveshaft shortened to fit my 727 tranny : 8-3/4 rear combo. The guy working on it wanted to know what the diameter of the u-joint seat is and the INside dimension of the pinion yoke is to build to fit. With dial calipers, the Inside dimension of the yoke reads 2.625"... Okay, that tells me it's a 7290 u-joint, BUT the diameter of the seat where the u-joint is housed is reading roughly 1.08"... That is for a 7260 u-joint. Is this possible ? The rear end is a 489 case from a '69 charger.