Each side can ping it's own gateway, but the gateways are set not to answer pings from outside. I suppose it might ping if the VPN made it an inside ping - I'll have to try that.

Both routers are happy that they have connected to each other with adequate authentication.

As to the addresses, stuff on the Internet is disorderly and mostly in the form of forums, but at least one specifically said the two had to be on different networks in the third stanza (but he presumed the default address for the router of 192.168.1.1, necessitating the other being 192.168.2.1 or some other). Anyway this is the configuration that connected.

Having them both on the same subnet (192.168.200.0) resulted in a configuration error in the router setup. Ranging (192.168.200.1 to 192.128.200.39 on one side and 192.168 200.40 to 192.168.200.100 on the other) resolved the conflict warning but didn't connect - but I think the no-connect was for another very obscure reason, so I may try ranging again tomorrow if I still can't see the other network.