Hi Rick,
Glad to be of assistance. being bounced around on the footplate of any engine (even a GWR one! ) is one of the highlights of my span in this corner of the galaxy (other chocolate bars are available). Mind you, the 4:30 am start? Not so much!
Regarding the use of chequer plate, my posited theory regarding the use of same has been consigned to the bin, thanks to Ozzyo's post above (#14). It's a good job there's folk around that can give you the pukka gen, rather than the (well-intentioned) speculative froth that comes from This Idiot.
Yes; the cut out for the brake standard is the chomped bit in your photos. Despite being down here in Plymuff, I'm not an authority on what sort of steel boxes sat behind the smoky bit of Swindon's finest; my niche is on the other side of the country, I'm afraid. So if your tender hasn't got a standard, I'd presume it wouldn't have a cut-out (thermal or otherwise).
As for whether my foot remembers the style of the crimping chunk, I've asked, and it's a non-starter, I'm afraid. I seem to recall (!!!WARNING: you are now entering a Minefield!!!) that a couple of the Hall's were smooth. But this - again - is speculation.
Cheers
Jan