For MGA, original floorboard screws are BMC# CPZ0416
Countersunk Pointed Zinc 1/4-28-UNF x 1
They are Phillips slotted screws, (Pozidriv screws were not introduced until after MGA was out of production).
The pointed tip can be a concours issue, even though a socket head or Phillips slotted head and flat washer may be hidden under carpet.

The washer is BMC part number 64401 Countersunk Cup Washer (zinc plated). This is similar to a finishing washer, except it has a wide flange around the outer edge to distribute the load over a wide area on the soft wood.

I used hex socket flat head screws with flat tips, just because that's what was conveniently available when I needed them, back in the late 70's when parts were harder to find. In place of the flat flange cup washers I used standard flat washers (3/8 size I think) and hit them with a countersink tool to make the screw heads lie flush.