I'm no expert on the Speedy 6 but here we go.
The speedmaster VI was originally designed by Fred Kiekhaefer back in the mid 80's when he was head of Kiekhaefer Aeromarine. It was released in 1988 as the Kiekhaefer K drive and only available to qualified race teams. Needless to say, it was a tremendous sucess. Mercury soon after bought out Kiekhaefer Aeromarine pretty much to gain the drive and re-named it the Speedmaster VI. Not sure when they were dry-sumped or the swept back skeg.