Last night I posted a rally compilation video that included a large old truck drifting a corner. I had no idea what it was but it blew my tiny little rally mind. I posted the video to Facebook as well, asking if anyone knew anything about what it was. Fortunately for me Finnish rally transplant Jari Hamalainen saw my post and was able to provide the answer.
Sure enough searching for "Gaz 51 rally" on youtube brought up a fair number of these trucks being rallied and rallycrossed. The drivers tend to really go for it, which seems a bit sketchy seeing as none of them have roll cages, just a large fortified rear roll hoop that sits behind (and sometimes over) the cab. That said I've found three videos in which these trucks take on trees and in all three the trees lose, so I'd probably still co-drive one.