The tab is spot welded to the water dam and the water dam is screwed to the floor. The water dam was only used in rumbleseat cars, so the water dam would have come from Ford with the tab spot-welded to it requiring only that the dealer then screw the water dam to the floor and the tabs would already be in place which would not require any grinding or welding to the floor. The reproduction water dams do not come with the tabs, but I believe that is just an oversight and believe that the water dams would have come from Ford with the tab in place.
The tab has to be on top of the water dam in both cases, otherwise the dam would have to be offset for clearance for the thickness of the tab to allow it to sit flat on the floor as it must to prevent water from running underneath it which is it's purpose.
In the factory rumbleseat cars I've seen, the front dowels were spotwelded but I have seen others with the dowels screwed or riveted which could have been dealer-installed rumbleseats.
Like most stuff with these early Fords, very little is written in stone. If the rumbleseat-dowel-welder was sick one day they could have riveted the dowels from the factory and it's just as likely that the dealer could have spotwelded the dowels because the tech preferred to do it that way.
My '33 standard with believed-to-be dealer installed rumbleseat does not even have the dowels, they left them off, no holes in floor so they were never installed, but it does have the tabs spot welded on top of the water dam.
On the car you're building, you would be most likely to be correct by spotwelding the dowels to the floor, spotwelding the tabs on top of the water dam and then screwing the water dam to the floor, in my opinion.
Randy
