OK CRG once again I need help.

In a previous thread I ask for help in trying to determine my rearend gearing because my speedo was off by 10mph on the high side 50 was actually 60, 30 is actually 40. It is suppose to be based on the numbers BP0403G2 a 2:73 or 3:08 built April 3rd in Detroit on the 2nd shift. I just had the car on a hoist and attempted to do it the old fashion way, mark my rear tire, put it in neutral ,marked the drive shaft and turned the tire one revolution and counted the turns on the drive shaft. Three times I did it and the shaft turned only 1 and 1/2 times!!!! We pulled the rear cover off the rear housing and I got these numbers off the ring gear, not sure this helps any, 1GM 3910823 underneath this is 15 11 ( or 41 ) 2 67. Is the 3910823 just the part number for the gear or what? Based on the old fashion turning I have a 1:1:50 rear gear!!!!!!!!!! Is this possible??

Help !!!!!!!!!!!!!!!!!

dab67

Dave