hi neil...i have a 3906 e-maxx, its was the very first version without the wide arms but is fitted with the proline widemaxx kit. i have ally bulkheads fitted to it. i thought i would buy ally diff casings and hardened crown wheel and pinion to do the job but was also looking at using 8th scale diffs also, which ever one is the toughest. thanks neil hope you are enjoying the sunshine down in sunny devon .