Looks like a 9-8 to me..? They are often the fastest or near to it on the SJ engines on sport speeders. I also had very good performance from 8.8 x 8.75 and 8.8 x 9 trimmed to around 8-3/8 on the SJ50. Weaker on launch but a bit more on the top.
CP if you need parts PM me..