Can I just weld in that toe board section from a manual donor cab?
Like Greg_H said, Yes you can weld in a manual tranny toe board section.
But here's the catch, the big removable hydra-matic tranny service panel floorboard cover
with the gas pedal attached to it, is wider than the manual tranny service panel floor board cover.So if you use the manual tranny service panel, you will ether have to extend both sides of the
floorboard tranny opening inward a couple inches or weld in reproduced manual tranny floorboard sheet metal to narrow the opening.
pic 1 right side
pic 2 left side
There are vendors that sell the Left & Right side with floorboard & toe board attached.
Left panel
Right panel I'm not sure but I think both the 3 & 4 speed tranny service panels are the same width.
Update:After I got my head out my butt.
All 47-55 1st series Hydra-Matic & Manual Transmission Service Cover/Panel are the same width.
Difference is the lengths.
1929 - 1957 Chevrolet Master Parts & Accessories Catalog says:
Group number 16.547 Cover, Transmission
47-55 1/2 3/4 TON (3 SPD),
15 3/4 wide x
20 1/4 long
47-55 1/2 3/4 TON (4 SPD),
15 3/4 wide x
20 long
54-55 COMM w/H.T. Trans,
15 3/4 wide x
34 7/8 long
1929-1957 Chevrolet MPC LINK Note:
1929-1954 Master Parts and Accessories Catalog,
Group number 16.547,
Does not have the Hydra-Matic Service Cover/Panel listed.