That's too bad about the Explore. We would have faced a similar issue had we needed to use the Explore test results as you have with grade versus what classes they are actually taking.
Our DD did 4-6th grade in school last year and then this year straddled 7th and 8th grade. When we applied we just submitted stuff and let them figure out what grade she should be in at the academy. We know our current school district isn't very high level, so we knew elsewhere she wouldn't have needed such a radical grade skip as she did here.
We used the WJ111 for the achievement test.
Is he a DYS? We used the same test results for DYS as for the academy. We were pretty much told that since she was already a DYS they knew she was smart enough, they wanted to see if she was academically ready for the school. They determined this on her teacher recommendations and during her assessment day.
Good luck!