Here's a pic of the J Pro.
Notice that the top deck on the J Pro only attaches to motor bulkhead in the rear via the chassis spring. The M2 Pro has two additional attachment points on the chassis on both sides of the bulkhead.
Also note the J Pro has two sets of holes on the motor bulkhead to allow mounting the layshaft both in the upper position (for stick packs) and the lower position (for saddle packs). The M2 Pro only allowed for mounting in the upper position and was anodized in blue. The J Pro only had clear anodizing.