Reviving an old thread, but I bought one of these off ebay because it said it was for a 383-400. I was out of town for a while and when it came i thought it visually looked too large for a B block, especially sitting side by side to a team g B block intake i had nearby. Measured the ports on it and it was exactly an inch wider port to port so it is for an RB block... and the ebay guy stuck me with it because I didn't realize it within 30 days :-( Just curious if you ever measured it to make sure it was B vs RB. Also, after reading this thread it sounds like I would have not been happy with it's performance anyways