But then I saw this
which clearly shows the motherboard and podule connectors on the same side. Chris's Acorns has an A500 and an A3xx b/p with the connectors where I expected them. So I let the seller know about those.
This has niggled, however, and sitting here I can see into the back of the R140 which happens to have been left out with no podules fitted. This has the "A440 UNIX backplane", podule sockets one side, motherboard connector the other. So I hypothesise ...
- other-side layout for A440/R140 and A3xx
- same-side layout for A680, A4x0/1 (plus later R140s based on the /1 model, even though labelled "A440, A410") and A5000
(A540/R2xx machines have a third layout)