If you want more detail on the front end, you might check out Adventure Cycling's Route 66 out of Santa Monica, and pick up their Grand Canyon Connector to head north. I suspect U.S. 89 is the best way to go north once you hit it (unless you want to check out a few other parks in southern Utah). @
greatbasin's suggestion to take UT 28 is probably a good one. Once you get to Utah Lake, there's supposed to be a MUP that'll take you to within a mile or two of the Tabernacle in SLC. I'm not sure if it's finished all the way south, though.