Click "Read More" for restoration and final result. (12/05/15: - Not yet, restoration just begun!)
A little bit of serendipity, or synchronicity: -
A few days later, when I was hunting for oval headed screws, I was in an establishment called Geoff's Emporium, when I happened to glance down the aisle, and there is a bloke looking through the stock of assorted nuts bolts screws washers etc. with notepaper and a set of calipers in hand. I don't think I have ever before in my life seen a customer with calipers in a shop.
Flat screws would need countersinking, and are pretty unforgiving if the drilled holes are not perfectly aligned with the plate holes. Also, if not drilled exactly vertical, an edge can sit proud, and you can see the face is not flat with the plate. They would be okay with just wood to wood.
Round heads are no good unless the shaft is exactly the hole diameter, to prevent the plate moving sideways, and then the domes would be too big.
Oval screws, on the other hand can have heads just bigger than the plate hole, will only stand proud without an edge, and can sit at a bit of an angle if not spot-on aligned, yet still pull in to the edges of the hole and keep the plate from moving sideways. They are the ones for this job, I reckon, even for the back where they can't be seen.
Can crusher design, Mark II.
I am an extremely intelligent, witty and fascinating guy.