Hi again Mike..based on the fact that I own one... know the Quicksilver boats and how they go together...work regularly with wood .. Im going to stick my neck out and say .. don’t waste more good money thinking a routed piece of hardwood will work.
However I have not made a wooden stringer..so if Fenlander has made one in the shape of the quicksilver one .. and it worked..then Im sure it will work for you too
IMO..the hardwood would splinter and break the first wave you went over.. due to the profile .. the slot in the side of the stringer .. required to fit the aluminium face plate on the floorboard will weaken the hardwood..and hardwood from my experience ..is very expensive and in thin sections.. splinters easily. Of course that is my opinion only.. feel free to go with the majority vote.
If I was in your position.. I would put thick tape over the edges of the aluminium trim on the floorboards... or possibly..better still..a piece of old hose pipe slit long ways ....if i couldn’t get proper plastic trim from B&Q or somewhere like that..that will cover the sharp edges on the floors. Put the floor in place.. blow up the tubes to pressure ..and bolt a piece of 1.5” square wood..soft or hard wood ..your choice.. along the stringer position length ..but inside the aluminium trims. That would hold your floor rigid..and the old hose pipe would protect your tubes from sharp edges. You could devise the bolts so you can unscrew them to disassemble the boa.
However the best thing would be to order the correct parts.. but that depends how flush you are and how you want to use the boat.
I cant get you an end profile as my boat is permanently set up and has too much internal junk..like consoles ..to take floors out...except at end of season. But here is the best view I can show..and in blue I have drawn a rough profile. The thickness below the slot is only a couple of mm.. hard wood would splinter very easily there.
Best of luck with the SIB.. I would have it in the water tomorrow if it were mine..and it would cost me around a quid or so for bolts..I have plenty scrap wood in my shed...and a bit of old hose