The machine now turns over beautifully, - light and silky. I used CRC spray, and a hot air gun to soften ancient sticky oil.
Quite satisfying, since I could hardly turn it when I first rescued it.
Now, see in that photo of the underside, there's a flat disc at bottom left. I'm wondering if that attaches to the back of the bobbin case, as in that shot of the bobbin case on the left, could that disc near the arrow head be that same disc part?
There is a tiny screw with it, and there's a slight bend/chamfer on the disc.
That bobbin case is the part I need, plus a rubber drivebelt, but that should be pretty easy eh?
The motor is mounted on the back of the pillar, so it's just a short round x-section rubber belt.
Meanwhile I'll pull the motor apart as it's rather noisy - bearings I'm sure.