8 3/4's were not available in a truck after '74. If the rear is truely out of a '79 then it is not an 8 3/4 and will either be an 8 1/4 or 9 1/4.
As far as the companies listed. I presently have Moser, Strange and Dutchman Axles and have had no issue with any of them. I have been using Dutchman recently because of their location. They are in Oregon and I am in Washington so I save on the freight costs.
