I believe the major differences are contained to the intake manifold and throttle body assembly, as well as the exhaust manifold and exhaust components. I'm surprised you had issues with the J35 at all, as its been a rather strong option for Honda for quite a few years. However, you should be able to run the 08 Odyssey engine if you swap over the intake manifold/throttle body from the Ridgeline, and re-use your stock exhaust manifolds.