I'm planning to homebrew a replacement for the missing trunk floor in my
solid axle late model TR-4A rather than buy one for $150.
Good luck. I did something similar - my 4A came with about half of
its trunk floor: the metal edging at the rear and some rotted fibreboard
attached to it.
1. How is the front of the trunk floor mounted to the chassis?
Your use of "front" and "rear" seems a bit ambiguous, so let me start over.
The original piece is 3/16" or so fibreboard (think Masonite) with
a steel strip at either end: one end near the fuel tank, one near
the rear bumper. I used plywood, instead, since Masonite has a habit
of absorbing water and getting soft.
The strip near the fuel tank is simple: It's a piece of thin (1/16" or so)
steel, bent at 90 degrees, rivetted to the fibreboard. I've never
seen an original, but I'd guess that it was rivetted to the bottom.
The vertical portion has rounded edges, to match the rounded cutout
at the bottom of the vertical panel that hides the fuel tank. The
portion on the underside isn't quite full width, so you don't have
additional thickness where the panel rests on the floor sheetmetal.
I made this piece out of an extruded aluminum angle, rivetted to the
bottom, with the corners rounded - it's thicker and stronger and was easier
than trying to make up the steel piece.
As you guessed, the panel fits under the clips that are visible. There
are meant to be two raised bolt heads surrounded by small cylinders
in the track that supports the panel - and holes to match in the
panel proper. This keeps the panel from wobbling around - in particular,
from sliding towards the bumper.
The bumper edge also gets a piece of steel, but a more complex one.
The panel extends to the edge where the floor sheet metal changes
from vertical to horizontal. There should be a male snap stud
on either side's horizontal surface. This is meant to attach to a
leather strap that is attached to the bumper-edge of the fibreboard
panel and holds the assembly down.
The steel assembly extends about 3/4" back on top, full width, and wraps
around the edge of the fibreboard. Underneath, as it makes the transition
from vertical to horizontal, it gets slightly narrower - again to avoid
metal-to-metal with the floor. Goes back about the same 3/4", then takes
a turn vertical about 1/8, horizontal about 1/2, then back vertical and
horizontal, making a stiffening rib. Two rows of rivets, one that
goes through both layers of steel (and the straps) and one that just
goes through the single layer underneath.
I had this piece, as I mentioned, or I probably wouldn't have tried
to make it. I would again take a piece of 90" extruded Al and mount
it underneath, pointing down, just for stiffening.
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