I also believe it is an 8R6 as well. I asked him if he measured the bore or not. I have a standard Model 8 from 1951 here, and it has a 2-1/4 inch bore. If it were a 2 inch bore, I would say it's either an NR6 or a 6R model.Mustie1 on YouTube just put out 3 videos on a Briggs gear reduction engine that I believe is a 8R6 model. Mustie 1 never figured out what engine he was working on, but because of the blower housing shape and the type of rope cup starter I believe it Is a model 8R6. It does not look like any type of model 6 or model 9 after comparing it to models I have.