Can you use the Teague MSD Brain Box bracked to mount on a HP 500 EFI, where it mounts to the back of the cylinder head.

Don't know if you can or not, but I would mount it on the transom away from direct engine heat.

If you have the oil cooler mounted across the upper rear of the engine above the bell housing, there is a clearance problem with the bracket that mounts the MSD on the back of the port side head. I had this problem when I switched to HP 500 coolers. I mounted my MSDs and rev limiters to the transom above and behind the distributors.

Seems to me you had a lot of clearance problems on the boat. I see your running though.