The wood die method suggested by Roy is valid. The method I've used was
often just a chunk of board with a radiused trough wallowed out in it.
The distortion isn't so great along the rib, but slightly greater at
the end of a rib, where the end forms a half-bowl (or the rib is a
junction of a Y or T shape).

Using just the blunted pick end of a bodywork hammer is a hell of a lot
of tapping, but it'll work if the forming process is gradual.

It sounds as though you have enough equipment to form the patches.
Establishing the parallel straight lines using a vise jaw edge or
similar straightedge, is a good starting point, then the rest of the
patch will draw into the trough in the die, or stretch as needed, as a
result of the small area of concentrated force delivered by the blunt
point of the hammer.

I haven't been involved in old car restoration for many years, and I'm
not familiar with all the sheetmetal products that are available today.
It wouldn't surprise me if a supplier is making ribbed steel in
continuous strips with flat margins on the sides, which could be
purchased, trimmed, and TIG/MIG'd into existing panels.

WB
...............

Ray Field wrote:
Metal worms have eaten a few holes in my '68 Austin front floors. Original
pans have half round stiffening ribs pressed into them.
Is there any simple method of reproducing these ribs in sheet metal 0.034 to
0.040 inch thick using hand tools, arbor press, heavy vice or other simple
workshop tools.
Ribs are semi circular cross section 3/8 inch radius, longest rib about 9
inches, other ribs same size are at right angle but separated by 3/4 inch
from cross rib. Will be making up patches about 9 inches square.
Any ideas or methodology will be appreciated (not car crusher or Jewish
lightning please).
Ray