I know about the old dive boards.
What they where was a lay on top fiberglass kayak of sorts. There was no seat. There was a hatch in the center or a hair forward of center that you could put your fish, weightbelt, spear guns, bottled water, etc.
It was a two part construction with a seam along the side. There were a few glassed in baffolds in the fore and aft sections of the center hold. They had a little keel at the back end and the bow was very narrow up highly upturned. This was so you caould go over bull kelp in a moderate swell and not pick up kelp if the bow dipped under.
They were propelled by laying on a slightly upsloped section right behind the hold and kicking with fins. There was no way to sit and use a paddle like a modern kayak. They were also very narrow and very long. Some boards were 20 feet long, others were from 12 to 16 feet.
Some brands were Litehall, Smith, and another one that escapes me now but restored one for a guy once that was 20 feet long. It weighed almost 100 pounds!
Those lay on spearfishing boards went out of fashion as soon as Ocean Kayak was born and came out with the Scupper Pro.
I know one guy who still swears by them and ownes three. He says by laying down you get out of the wind better and can make headway very easily. He also claims they are fast becase they are long. But to me having to fin those things, then fin some more when you start diving, then finning again to get back to the beach. That just seems like a lot of work.
I like my kayak, I can kick back and eat lunch, paddle around, fish off it, scuba dive off it, and freedive/ab dive off it.