I had the 69' GMC on the lift this weekend and got the casting numbers off the differential housing - C30255. But I couldn't find anything on Google to help understand the numbers. I did find an article on GM RPO numbers, and looked as directed, but no info on the differential. And there was not tag on one of the bolts. Doesn't look like a complete assembly swap, but no history.
Also have another question; say the plug to check oil level, but how do you drain it for a fresh oil change?
