I quit using speed screws on trailer decks a long time ago. That's a production speed thing. No need for a DIY r4epair. I just grind/cut the old ones off flush with the frame. Then slip the plank in and drill 1/4" down through the wood and frame flange. Carriage bolt and nylock on the bottom. Two for the front and rear frames if they are not tuck-in style. Alternate sides of the planks for bolts for the intermediate frames.
For HD tilt beads that will carry track equipment, I switch up to 3/8 bolts, same schedule. But I counter bore the top of the plank so the head is recessed so a tracks can't catch a bolt head and pull it out. Slop Cuprinol in the head pocket to stop debris rot from starting and bolt them down.
I switched to 2x12's a long time ago where the wheel or track loads are, skinnier planks only in the middle. The 2x12's bridge the frames better under load w/o splitting or breaking. That's why the alternate side bolt pattern to stop the expansion and shrinkage stresses from splitting the planks summer and winter.
In your case, you have tuck-in plank butts on the back end that float, so they should resist splitting well there