I though "thought" was thought, putted thouth, but its though. I though wrong :D
I really dont know. If i had the will, and the time, i would try it.

Few novel ideas are any good raw.

Let's dispense with the sheet metal case sides altogether - and build those sides out of radiator. We could have two radiators/side walls, or a single rad going up one side, over the top, and down the other side.

Delicate fins would need some kind of cage to protect them from mechanical harm... this is looking bulky.

Maybe lots of square tubes which are cheap and readily available (say 1/4" thick, brass or aluminum for toughness) bonded side-by-side to form a solid wall? I'm imagining something you can get as a sheet good and cut to size, then cap off with a simple kit.

Thats an idea that i had also.
But it had to be heatercores or else all those meters of tube would be very restictive.

In parallel?

Never liked parallel. The water would only pass "trough" (ahah!) one rad instead of them all.
But them you would have much lower restriction.
But you dont know if the water is even passing trough the most restrictive rad.
But probably would pass, but with lower flow.

I would prefer some low-restricting heatercores in series. But its all a matter of choise.