I have taken this road into Yosemite valley twice from Coulterville. It took about four hours. This includes trying to get around downed trees and taking the wrong loop once.. or twice? It is largely unpaved but there are areas where pavement appears out of nowhere. Bring a chain saw, and your 4 wheel drive if you want to do it. It may take some time, bring food water, blankets, too. You might not see anyone for a long time out there. I think it's called Old Coulterville road, or county 1S12. It lies between the current day routes of 140 and 120.
Either way, start out where the monument is stating it was built in 1874, continue on up. if you can find the correct left turn at Buena Vista Junction, then a hairpin turn down into a seasonal creek bed, into some dense woods and you pop out into Foresta. From there, the old road goes through Foresta, and as you climb back up out of Foresta and toward the 120 descent (which of course did not exist in the day), there on your right is the Old Coulterville Road entrance to the valley floor. It has a few large boulders placed there by the NPS. This is the section of the road that is permanently closed and the rockslide took out the lower third in around 1981. You can see it clearly from the other side of the valley up on Wawona road. I have hiked this part down to the valley floor. I don't think I will again. The last part through the boulder field is particularly difficult and risky. But anyway I have driven in from hwy 49, through Coulterville and through Foresta. I've done it twice, it does go through and it was a lot of fun. And no, there is no entrance gate there. I have never left the park via this route.