Yes!

I made up the 3 ribbon cables today for the 3 stepper motor driver boards. As I did so, it occurred to me that the cables connected these boards to the motherboard, and that as the cables had the same connectors on either end, the motherboard must have an IDC header, which is the part I ordered singly, instead of a set of 3.
Sooooooooo, I nicked the header from the motherboard kit in order to make up the second board.

On positioning the parts for the second stepper motor driver board, I was careful to orient the chip correctly!

When I cooked the second board, I did so withOUT the large electrolytic capacitors in place.
I cooked on medium to heat the board up and then as soon as the solder paste started to melt I turned it up to medium high. All told, it took just over 3 minutes. Nothing moved at all. There was distinctly more smell this time - last time was almost smell-free.

On cooling, I checked all the contacts from the chip (which was perfect, with no bridges at all) along the traces as drawn on the board. I removed the solder balls with the back of the knife blade again, and checked the resistance across all of the solder mount resistors from solder to solder. All was well. I had just one capacitor that had made good electrical connection but was not good mechanically, having far too little solder. I put the tiniest bit of paste on that end and used the soldering iron with chisel tip to make it good. I also used paste to solder the electrolytic capacitors in place, carefully positioning C11 as far away from the end of the chip as possible whilst leaving exposed solder at the other end of the capacitor to facilitate soldering.

I then ordered 2 more headers for the next board and the motherboard, and a replacement driver chip from Farnell.

I soldered in the stand-in giant resistors, and the through-hole components (with the nicked IDC header), and inspected and tested everything (that I could follow and understand).

JOY! This time, no drama, and the power LED lit up. Yes!
Now I have to wait for my next Farnell delivery before I can do the third board.